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-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
-<html>
-<head>
-<title>Lua 5.1 Reference Manual</title>
-<link rel="stylesheet" type="text/css" href="lua.css">
-<link rel="stylesheet" type="text/css" href="manual.css">
-<META HTTP-EQUIV="content-type" CONTENT="text/html; charset=iso-8859-1">
-</head>
-<body>
-<hr>
-<h1>
-<a href="http://www.lua.org/"><img src="logo.gif" alt="" border="0"></a>
-Lua 5.1 Reference Manual
-</h1>
-by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes
-<p>
-<small>
-Copyright &copy; 2006-2008 Lua.org, PUC-Rio.
-Freely available under the terms of the
-<a href="http://www.lua.org/license.html#5">Lua license</a>.
-</small>
-<hr>
-<p>
-<a href="contents.html#contents">contents</A>
-&middot;
-<a href="contents.html#index">index</A>
-<!-- ====================================================================== -->
-<p>
-<!-- $Id: manual.of,v 1.48 2008/08/18 15:24:20 roberto Exp $ -->
-<h1>1 - <a name="1">Introduction</a></h1>
-<p>
-Lua is an extension programming language designed to support
-general procedural programming with data description
-facilities.
-It also offers good support for object-oriented programming,
-functional programming, and data-driven programming.
-Lua is intended to be used as a powerful, light-weight
-scripting language for any program that needs one.
-Lua is implemented as a library, written in <em>clean</em> C
-(that is, in the common subset of ANSI&nbsp;C and C++).
-<p>
-Being an extension language, Lua has no notion of a "main" program:
-it only works <em>embedded</em> in a host client,
-called the <em>embedding program</em> or simply the <em>host</em>.
-This host program can invoke functions to execute a piece of Lua code,
-can write and read Lua variables,
-and can register C&nbsp;functions to be called by Lua code.
-Through the use of C&nbsp;functions, Lua can be augmented to cope with
-a wide range of different domains,
-thus creating customized programming languages sharing a syntactical framework.
-The Lua distribution includes a sample host program called <code>lua</code>,
-which uses the Lua library to offer a complete, stand-alone Lua interpreter.
-<p>
-Lua is free software,
-and is provided as usual with no guarantees,
-as stated in its license.
-The implementation described in this manual is available
-at Lua's official web site, <code>www.lua.org</code>.
-<p>
-Like any other reference manual,
-this document is dry in places.
-For a discussion of the decisions behind the design of Lua,
-see the technical papers available at Lua's web site.
-For a detailed introduction to programming in Lua,
-see Roberto's book, <em>Programming in Lua (Second Edition)</em>.
-<h1>2 - <a name="2">The Language</a></h1>
-<p>
-This section describes the lexis, the syntax, and the semantics of Lua.
-In other words,
-this section describes
-which tokens are valid,
-how they can be combined,
-and what their combinations mean.
-<p>
-The language constructs will be explained using the usual extended BNF notation,
-in which
-{<em>a</em>}&nbsp;means&nbsp;0 or more <em>a</em>'s, and
-[<em>a</em>]&nbsp;means an optional <em>a</em>.
-Non-terminals are shown like non-terminal,
-keywords are shown like <b>kword</b>,
-and other terminal symbols are shown like `<b>=</b>&acute;.
-The complete syntax of Lua can be found in <a href="#8">&sect;8</a>
-at the end of this manual.
-<h2>2.1 - <a name="2.1">Lexical Conventions</a></h2>
-<p>
-<em>Names</em>
-(also called <em>identifiers</em>)
-in Lua can be any string of letters,
-digits, and underscores,
-not beginning with a digit.
-This coincides with the definition of names in most languages.
-(The definition of letter depends on the current locale:
-any character considered alphabetic by the current locale
-can be used in an identifier.)
-Identifiers are used to name variables and table fields.
-<p>
-The following <em>keywords</em> are reserved
-and cannot be used as names:
-<pre>
-     and       break     do        else      elseif
-     end       false     for       function  if
-     in        local     nil       not       or
-     repeat    return    then      true      until     while
-</pre>
-<p>
-Lua is a case-sensitive language:
-<code>and</code> is a reserved word, but <code>And</code> and <code>AND</code>
-are two different, valid names.
-As a convention, names starting with an underscore followed by
-uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>)
-are reserved for internal global variables used by Lua.
-<p>
-The following strings denote other tokens:
-<pre>
-     +     -     *     /     %     ^     #
-     ==    ~=    &lt;=    &gt;=    &lt;     &gt;     =
-     (     )     {     }     [     ]
-     ;     :     ,     .     ..    ...
-</pre>
-<p>
-<em>Literal strings</em>
-can be delimited by matching single or double quotes,
-and can contain the following C-like escape sequences:
-'<code>\a</code>' (bell),
-'<code>\b</code>' (backspace),
-'<code>\f</code>' (form feed),
-'<code>\n</code>' (newline),
-'<code>\r</code>' (carriage return),
-'<code>\t</code>' (horizontal tab),
-'<code>\v</code>' (vertical tab),
-'<code>\\</code>' (backslash),
-'<code>\"</code>' (quotation mark [double quote]),
-and '<code>\'</code>' (apostrophe [single quote]).
-Moreover, a backslash followed by a real newline
-results in a newline in the string.
-A character in a string can also be specified by its numerical value
-using the escape sequence <code>\<em>ddd</em></code>,
-where <em>ddd</em> is a sequence of up to three decimal digits.
-(Note that if a numerical escape is to be followed by a digit,
-it must be expressed using exactly three digits.)
-Strings in Lua can contain any 8-bit value, including embedded zeros,
-which can be specified as '<code>\0</code>'.
-<p>
-Literal strings can also be defined using a long format
-enclosed by <em>long brackets</em>.
-We define an <em>opening long bracket of level <em>n</em></em> as an opening
-square bracket followed by <em>n</em> equal signs followed by another
-opening square bracket.
-So, an opening long bracket of level&nbsp;0 is written as <code>[[</code>,
-an opening long bracket of level&nbsp;1 is written as <code>[=[</code>,
-and so on.
-A <em>closing long bracket</em> is defined similarly;
-for instance, a closing long bracket of level&nbsp;4 is written as <code>]====]</code>.
-A long string starts with an opening long bracket of any level and
-ends at the first closing long bracket of the same level.
-Literals in this bracketed form can run for several lines,
-do not interpret any escape sequences,
-and ignore long brackets of any other level.
-They can contain anything except a closing bracket of the proper level.
-<p>
-For convenience,
-when the opening long bracket is immediately followed by a newline,
-the newline is not included in the string.
-As an example, in a system using ASCII
-(in which '<code>a</code>' is coded as&nbsp;97,
-newline is coded as&nbsp;10, and '<code>1</code>' is coded as&nbsp;49),
-the five literal strings below denote the same string:
-<pre>
-     a = 'alo\n123"'
-     a = "alo\n123\""
-     a = '\97lo\10\04923"'
-     a = [[alo
-     123"]]
-     a = [==[
-     alo
-     123"]==]
-</pre>
-<p>
-A <em>numerical constant</em> can be written with an optional decimal part
-and an optional decimal exponent.
-Lua also accepts integer hexadecimal constants,
-by prefixing them with <code>0x</code>.
-Examples of valid numerical constants are
-<pre>
-     3   3.0   3.1416   314.16e-2   0.31416E1   0xff   0x56
-</pre>
-<p>
-A <em>comment</em> starts with a double hyphen (<code>--</code>)
-anywhere outside a string.
-If the text immediately after <code>--</code> is not an opening long bracket,
-the comment is a <em>short comment</em>,
-which runs until the end of the line.
-Otherwise, it is a <em>long comment</em>,
-which runs until the corresponding closing long bracket.
-Long comments are frequently used to disable code temporarily.
-<h2>2.2 - <a name="2.2">Values and Types</a></h2>
-<p>
-Lua is a <em>dynamically typed language</em>.
-This means that
-variables do not have types; only values do.
-There are no type definitions in the language.
-All values carry their own type.
-<p>
-All values in Lua are <em>first-class values</em>.
-This means that all values can be stored in variables,
-passed as arguments to other functions, and returned as results.
-<p>
-There are eight basic types in Lua:
-<em>nil</em>, <em>boolean</em>, <em>number</em>,
-<em>string</em>, <em>function</em>, <em>userdata</em>,
-<em>thread</em>, and <em>table</em>.
-<em>Nil</em> is the type of the value <b>nil</b>,
-whose main property is to be different from any other value;
-it usually represents the absence of a useful value.
-<em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>.
-Both <b>nil</b> and <b>false</b> make a condition false;
-any other value makes it true.
-<em>Number</em> represents real (double-precision floating-point) numbers.
-(It is easy to build Lua interpreters that use other
-internal representations for numbers,
-such as single-precision float or long integers;
-see file <code>luaconf.h</code>.)
-<em>String</em> represents arrays of characters.
-Lua is 8-bit clean:
-strings can contain any 8-bit character,
-including embedded zeros ('<code>\0</code>') (see <a href="#2.1">&sect;2.1</a>).
-<p>
-Lua can call (and manipulate) functions written in Lua and
-functions written in C
-(see <a href="#2.5.8">&sect;2.5.8</a>).
-<p>
-The type <em>userdata</em> is provided to allow arbitrary C&nbsp;data to
-be stored in Lua variables.
-This type corresponds to a block of raw memory
-and has no pre-defined operations in Lua,
-except assignment and identity test.
-However, by using <em>metatables</em>,
-the programmer can define operations for userdata values
-(see <a href="#2.8">&sect;2.8</a>).
-Userdata values cannot be created or modified in Lua,
-only through the C&nbsp;API.
-This guarantees the integrity of data owned by the host program.
-<p>
-The type <em>thread</em> represents independent threads of execution
-and it is used to implement coroutines (see <a href="#2.11">&sect;2.11</a>).
-Do not confuse Lua threads with operating-system threads.
-Lua supports coroutines on all systems,
-even those that do not support threads.
-<p>
-The type <em>table</em> implements associative arrays,
-that is, arrays that can be indexed not only with numbers,
-but with any value (except <b>nil</b>).
-Tables can be <em>heterogeneous</em>;
-that is, they can contain values of all types (except <b>nil</b>).
-Tables are the sole data structuring mechanism in Lua;
-they can be used to represent ordinary arrays,
-symbol tables, sets, records, graphs, trees, etc.
-To represent records, Lua uses the field name as an index.
-The language supports this representation by
-providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>.
-There are several convenient ways to create tables in Lua
-(see <a href="#2.5.7">&sect;2.5.7</a>).
-<p>
-Like indices,
-the value of a table field can be of any type (except <b>nil</b>).
-In particular,
-because functions are first-class values,
-table fields can contain functions.
-Thus tables can also carry <em>methods</em> (see <a href="#2.5.9">&sect;2.5.9</a>).
-<p>
-Tables, functions, threads, and (full) userdata values are <em>objects</em>:
-variables do not actually <em>contain</em> these values,
-only <em>references</em> to them.
-Assignment, parameter passing, and function returns
-always manipulate references to such values;
-these operations do not imply any kind of copy.
-<p>
-The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type
-of a given value.
-<h3>2.2.1 - <a name="2.2.1">Coercion</a></h3>
-<p>
-Lua provides automatic conversion between
-string and number values at run time.
-Any arithmetic operation applied to a string tries to convert
-this string to a number, following the usual conversion rules.
-Conversely, whenever a number is used where a string is expected,
-the number is converted to a string, in a reasonable format.
-For complete control over how numbers are converted to strings,
-use the <code>format</code> function from the string library
-(see <a href="#pdf-string.format"><code>string.format</code></a>).
-<h2>2.3 - <a name="2.3">Variables</a></h2>
-<p>
-Variables are places that store values.
-There are three kinds of variables in Lua:
-global variables, local variables, and table fields.
-<p>
-A single name can denote a global variable or a local variable
-(or a function's formal parameter,
-which is a particular kind of local variable):
-<pre>
-        var ::= Name
-</pre><p>
-Name denotes identifiers, as defined in <a href="#2.1">&sect;2.1</a>.
-<p>
-Any variable is assumed to be global unless explicitly declared
-as a local (see <a href="#2.4.7">&sect;2.4.7</a>).
-Local variables are <em>lexically scoped</em>:
-local variables can be freely accessed by functions
-defined inside their scope (see <a href="#2.6">&sect;2.6</a>).
-<p>
-Before the first assignment to a variable, its value is <b>nil</b>.
-<p>
-Square brackets are used to index a table:
-<pre>
-        var ::= prefixexp `<b>[</b>&acute; exp `<b>]</b>&acute;
-</pre><p>
-The meaning of accesses to global variables 
-and table fields can be changed via metatables.
-An access to an indexed variable <code>t[i]</code> is equivalent to
-a call <code>gettable_event(t,i)</code>.
-(See <a href="#2.8">&sect;2.8</a> for a complete description of the
-<code>gettable_event</code> function.
-This function is not defined or callable in Lua.
-We use it here only for explanatory purposes.)
-<p>
-The syntax <code>var.Name</code> is just syntactic sugar for
-<code>var["Name"]</code>:
-<pre>
-        var ::= prefixexp `<b>.</b>&acute; Name
-</pre>
-<p>
-All global variables live as fields in ordinary Lua tables,
-called <em>environment tables</em> or simply
-<em>environments</em> (see <a href="#2.9">&sect;2.9</a>).
-Each function has its own reference to an environment,
-so that all global variables in this function
-will refer to this environment table.
-When a function is created,
-it inherits the environment from the function that created it.
-To get the environment table of a Lua function,
-you call <a href="#pdf-getfenv"><code>getfenv</code></a>.
-To replace it,
-you call <a href="#pdf-setfenv"><code>setfenv</code></a>.
-(You can only manipulate the environment of C&nbsp;functions
-through the debug library; (see <a href="#5.9">&sect;5.9</a>).)
-<p>
-An access to a global variable <code>x</code>
-is equivalent to <code>_env.x</code>,
-which in turn is equivalent to
-<pre>
-     gettable_event(_env, "x")
-</pre><p>
-where <code>_env</code> is the environment of the running function.
-(See <a href="#2.8">&sect;2.8</a> for a complete description of the
-<code>gettable_event</code> function.
-This function is not defined or callable in Lua.
-Similarly, the <code>_env</code> variable is not defined in Lua.
-We use them here only for explanatory purposes.)
-<h2>2.4 - <a name="2.4">Statements</a></h2>
-<p>
-Lua supports an almost conventional set of statements,
-similar to those in Pascal or C.
-This set includes
-assignments, control structures, function calls,
-and variable declarations.
-<h3>2.4.1 - <a name="2.4.1">Chunks</a></h3>
-<p>
-The unit of execution of Lua is called a <em>chunk</em>.
-A chunk is simply a sequence of statements,
-which are executed sequentially.
-Each statement can be optionally followed by a semicolon:
-<pre>
-        chunk ::= {stat [`<b>;</b>&acute;]}
-</pre><p>
-There are no empty statements and thus '<code>;;</code>' is not legal.
-<p>
-Lua handles a chunk as the body of an anonymous function 
-with a variable number of arguments
-(see <a href="#2.5.9">&sect;2.5.9</a>).
-As such, chunks can define local variables,
-receive arguments, and return values.
-<p>
-A chunk can be stored in a file or in a string inside the host program.
-To execute a chunk,
-Lua first pre-compiles the chunk into instructions for a virtual machine,
-and then it executes the compiled code
-with an interpreter for the virtual machine.
-<p>
-Chunks can also be pre-compiled into binary form;
-see program <code>luac</code> for details.
-Programs in source and compiled forms are interchangeable;
-Lua automatically detects the file type and acts accordingly.
-<h3>2.4.2 - <a name="2.4.2">Blocks</a></h3><p>
-A block is a list of statements;
-syntactically, a block is the same as a chunk:
-<pre>
-        block ::= chunk
-</pre>
-<p>
-A block can be explicitly delimited to produce a single statement:
-<pre>
-        stat ::= <b>do</b> block <b>end</b>
-</pre><p>
-Explicit blocks are useful
-to control the scope of variable declarations.
-Explicit blocks are also sometimes used to
-add a <b>return</b> or <b>break</b> statement in the middle
-of another block (see <a href="#2.4.4">&sect;2.4.4</a>).
-<h3>2.4.3 - <a name="2.4.3">Assignment</a></h3>
-<p>
-Lua allows multiple assignments.
-Therefore, the syntax for assignment
-defines a list of variables on the left side
-and a list of expressions on the right side.
-The elements in both lists are separated by commas:
-<pre>
-        stat ::= varlist `<b>=</b>&acute; explist
-        varlist ::= var {`<b>,</b>&acute; var}
-        explist ::= exp {`<b>,</b>&acute; exp}
-</pre><p>
-Expressions are discussed in <a href="#2.5">&sect;2.5</a>.
-<p>
-Before the assignment,
-the list of values is <em>adjusted</em> to the length of
-the list of variables.
-If there are more values than needed,
-the excess values are thrown away.
-If there are fewer values than needed,
-the list is extended with as many  <b>nil</b>'s as needed.
-If the list of expressions ends with a function call,
-then all values returned by that call enter the list of values,
-before the adjustment
-(except when the call is enclosed in parentheses; see <a href="#2.5">&sect;2.5</a>).
-<p>
-The assignment statement first evaluates all its expressions
-and only then are the assignments performed.
-Thus the code
-<pre>
-     i = 3
-     i, a[i] = i+1, 20
-</pre><p>
-sets <code>a[3]</code> to 20, without affecting <code>a[4]</code>
-because the <code>i</code> in <code>a[i]</code> is evaluated (to 3)
-before it is assigned&nbsp;4.
-Similarly, the line
-<pre>
-     x, y = y, x
-</pre><p>
-exchanges the values of <code>x</code> and <code>y</code>,
-and
-<pre>
-     x, y, z = y, z, x
-</pre><p>
-cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>.
-<p>
-The meaning of assignments to global variables
-and table fields can be changed via metatables.
-An assignment to an indexed variable <code>t[i] = val</code> is equivalent to
-<code>settable_event(t,i,val)</code>.
-(See <a href="#2.8">&sect;2.8</a> for a complete description of the
-<code>settable_event</code> function.
-This function is not defined or callable in Lua.
-We use it here only for explanatory purposes.)
-<p>
-An assignment to a global variable <code>x = val</code>
-is equivalent to the assignment
-<code>_env.x = val</code>,
-which in turn is equivalent to
-<pre>
-     settable_event(_env, "x", val)
-</pre><p>
-where <code>_env</code> is the environment of the running function.
-(The <code>_env</code> variable is not defined in Lua.
-We use it here only for explanatory purposes.)
-<h3>2.4.4 - <a name="2.4.4">Control Structures</a></h3><p>
-The control structures
-<b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and
-familiar syntax:
-<pre>
-        stat ::= <b>while</b> exp <b>do</b> block <b>end</b>
-        stat ::= <b>repeat</b> block <b>until</b> exp
-        stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b>
-</pre><p>
-Lua also has a <b>for</b> statement, in two flavors (see <a href="#2.4.5">&sect;2.4.5</a>).
-<p>
-The condition expression of a
-control structure can return any value.
-Both <b>false</b> and <b>nil</b> are considered false.
-All values different from <b>nil</b> and <b>false</b> are considered true
-(in particular, the number 0 and the empty string are also true).
-<p>
-In the <b>repeat</b>&ndash;<b>until</b> loop,
-the inner block does not end at the <b>until</b> keyword,
-but only after the condition.
-So, the condition can refer to local variables
-declared inside the loop block.
-<p>
-The <b>return</b> statement is used to return values
-from a function or a chunk (which is just a function).
-Functions and chunks can return more than one value,
-and so the syntax for the <b>return</b> statement is
-<pre>
-        stat ::= <b>return</b> [explist]
-</pre>
-<p>
-The <b>break</b> statement is used to terminate the execution of a
-<b>while</b>, <b>repeat</b>, or <b>for</b> loop,
-skipping to the next statement after the loop:
-<pre>
-        stat ::= <b>break</b>
-</pre><p>
-A <b>break</b> ends the innermost enclosing loop.
-<p>
-The <b>return</b> and <b>break</b>
-statements can only be written as the <em>last</em> statement of a block.
-If it is really necessary to <b>return</b> or <b>break</b> in the
-middle of a block,
-then an explicit inner block can be used,
-as in the idioms
-<code>do return end</code> and <code>do break end</code>,
-because now <b>return</b> and <b>break</b> are the last statements in
-their (inner) blocks.
-<h3>2.4.5 - <a name="2.4.5">For Statement</a></h3>
-<p>
-The <b>for</b> statement has two forms:
-one numeric and one generic.
-<p>
-The numeric <b>for</b> loop repeats a block of code while a
-control variable runs through an arithmetic progression.
-It has the following syntax:
-<pre>
-        stat ::= <b>for</b> Name `<b>=</b>&acute; exp `<b>,</b>&acute; exp [`<b>,</b>&acute; exp] <b>do</b> block <b>end</b>
-</pre><p>
-The <em>block</em> is repeated for <em>name</em> starting at the value of
-the first <em>exp</em>, until it passes the second <em>exp</em> by steps of the
-third <em>exp</em>.
-More precisely, a <b>for</b> statement like
-<pre>
-     for v = <em>e1</em>, <em>e2</em>, <em>e3</em> do <em>block</em> end
-</pre><p>
-is equivalent to the code:
-<pre>
-     do
-       local <em>var</em>, <em>limit</em>, <em>step</em> = tonumber(<em>e1</em>), tonumber(<em>e2</em>), tonumber(<em>e3</em>)
-       if not (<em>var</em> and <em>limit</em> and <em>step</em>) then error() end
-       while (<em>step</em> &gt; 0 and <em>var</em> &lt;= <em>limit</em>) or (<em>step</em> &lt;= 0 and <em>var</em> &gt;= <em>limit</em>) do
-         local v = <em>var</em>
-         <em>block</em>
-         <em>var</em> = <em>var</em> + <em>step</em>
-       end
-     end
-</pre><p>
-Note the following:
-<ul>
-<li>
-All three control expressions are evaluated only once,
-before the loop starts.
-They must all result in numbers.
-</li>
-<li>
-<code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables.
-The names shown here are for explanatory purposes only.
-</li>
-<li>
-If the third expression (the step) is absent,
-then a step of&nbsp;1 is used.
-</li>
-<li>
-You can use <b>break</b> to exit a <b>for</b> loop.
-</li>
-<li>
-The loop variable <code>v</code> is local to the loop;
-you cannot use its value after the <b>for</b> ends or is broken.
-If you need this value,
-assign it to another variable before breaking or exiting the loop.
-</li>
-</ul>
-<p>
-The generic <b>for</b> statement works over functions,
-called <em>iterators</em>.
-On each iteration, the iterator function is called to produce a new value,
-stopping when this new value is <b>nil</b>.
-The generic <b>for</b> loop has the following syntax:
-<pre>
-        stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b>
-        namelist ::= Name {`<b>,</b>&acute; Name}
-</pre><p>
-A <b>for</b> statement like
-<pre>
-     for <em>var_1</em>, &middot;&middot;&middot;, <em>var_n</em> in <em>explist</em> do <em>block</em> end
-</pre><p>
-is equivalent to the code:
-<pre>
-     do
-       local <em>f</em>, <em>s</em>, <em>var</em> = <em>explist</em>
-       while true do
-         local <em>var_1</em>, &middot;&middot;&middot;, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>)
-         <em>var</em> = <em>var_1</em>
-         if <em>var</em> == nil then break end
-         <em>block</em>
-       end
-     end
-</pre><p>
-Note the following:
-<ul>
-<li>
-<code><em>explist</em></code> is evaluated only once.
-Its results are an <em>iterator</em> function,
-a <em>state</em>,
-and an initial value for the first <em>iterator variable</em>.
-</li>
-<li>
-<code><em>f</em></code>, <code><em>s</em></code>, and <code><em>var</em></code> are invisible variables.
-The names are here for explanatory purposes only.
-</li>
-<li>
-You can use <b>break</b> to exit a <b>for</b> loop.
-</li>
-<li>
-The loop variables <code><em>var_i</em></code> are local to the loop;
-you cannot use their values after the <b>for</b> ends.
-If you need these values,
-then assign them to other variables before breaking or exiting the loop.
-</li>
-</ul>
-<h3>2.4.6 - <a name="2.4.6">Function Calls as Statements</a></h3><p>
-To allow possible side-effects,
-function calls can be executed as statements:
-<pre>
-        stat ::= functioncall
-</pre><p>
-In this case, all returned values are thrown away.
-Function calls are explained in <a href="#2.5.8">&sect;2.5.8</a>.
-<h3>2.4.7 - <a name="2.4.7">Local Declarations</a></h3><p>
-Local variables can be declared anywhere inside a block.
-The declaration can include an initial assignment:
-<pre>
-        stat ::= <b>local</b> namelist [`<b>=</b>&acute; explist]
-</pre><p>
-If present, an initial assignment has the same semantics
-of a multiple assignment (see <a href="#2.4.3">&sect;2.4.3</a>).
-Otherwise, all variables are initialized with <b>nil</b>.
-<p>
-A chunk is also a block (see <a href="#2.4.1">&sect;2.4.1</a>),
-and so local variables can be declared in a chunk outside any explicit block.
-The scope of such local variables extends until the end of the chunk.
-<p>
-The visibility rules for local variables are explained in <a href="#2.6">&sect;2.6</a>.
-<h2>2.5 - <a name="2.5">Expressions</a></h2>
-<p>
-The basic expressions in Lua are the following:
-<pre>
-        exp ::= prefixexp
-        exp ::= <b>nil</b> | <b>false</b> | <b>true</b>
-        exp ::= Number
-        exp ::= String
-        exp ::= function
-        exp ::= tableconstructor
-        exp ::= `<b>...</b>&acute;
-        exp ::= exp binop exp
-        exp ::= unop exp
-        prefixexp ::= var | functioncall | `<b>(</b>&acute; exp `<b>)</b>&acute;
-</pre>
-<p>
-Numbers and literal strings are explained in <a href="#2.1">&sect;2.1</a>;
-variables are explained in <a href="#2.3">&sect;2.3</a>;
-function definitions are explained in <a href="#2.5.9">&sect;2.5.9</a>;
-function calls are explained in <a href="#2.5.8">&sect;2.5.8</a>;
-table constructors are explained in <a href="#2.5.7">&sect;2.5.7</a>.
-Vararg expressions,
-denoted by three dots ('<code>...</code>'), can only be used when
-directly inside a vararg function;
-they are explained in <a href="#2.5.9">&sect;2.5.9</a>.
-<p>
-Binary operators comprise arithmetic operators (see <a href="#2.5.1">&sect;2.5.1</a>),
-relational operators (see <a href="#2.5.2">&sect;2.5.2</a>), logical operators (see <a href="#2.5.3">&sect;2.5.3</a>),
-and the concatenation operator (see <a href="#2.5.4">&sect;2.5.4</a>).
-Unary operators comprise the unary minus (see <a href="#2.5.1">&sect;2.5.1</a>),
-the unary <b>not</b> (see <a href="#2.5.3">&sect;2.5.3</a>),
-and the unary <em>length operator</em> (see <a href="#2.5.5">&sect;2.5.5</a>).
-<p>
-Both function calls and vararg expressions can result in multiple values.
-If an expression is used as a statement
-(only possible for function calls (see <a href="#2.4.6">&sect;2.4.6</a>)),
-then its return list is adjusted to zero elements,
-thus discarding all returned values.
-If an expression is used as the last (or the only) element
-of a list of expressions,
-then no adjustment is made
-(unless the call is enclosed in parentheses).
-In all other contexts,
-Lua adjusts the result list to one element,
-discarding all values except the first one.
-<p>
-Here are some examples:
-<pre>
-     f()                -- adjusted to 0 results
-     g(f(), x)          -- f() is adjusted to 1 result
-     g(x, f())          -- g gets x plus all results from f()
-     a,b,c = f(), x     -- f() is adjusted to 1 result (c gets nil)
-     a,b = ...          -- a gets the first vararg parameter, b gets
-                        -- the second (both a and b can get nil if there
-                        -- is no corresponding vararg parameter)
-     
-     a,b,c = x, f()     -- f() is adjusted to 2 results
-     a,b,c = f()        -- f() is adjusted to 3 results
-     return f()         -- returns all results from f()
-     return ...         -- returns all received vararg parameters
-     return x,y,f()     -- returns x, y, and all results from f()
-     {f()}              -- creates a list with all results from f()
-     {...}              -- creates a list with all vararg parameters
-     {f(), nil}         -- f() is adjusted to 1 result
-</pre>
-<p>
-Any expression enclosed in parentheses always results in only one value.
-Thus,
-<code>(f(x,y,z))</code> is always a single value,
-even if <code>f</code> returns several values.
-(The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code>
-or <b>nil</b> if <code>f</code> does not return any values.)
-<h3>2.5.1 - <a name="2.5.1">Arithmetic Operators</a></h3><p>
-Lua supports the usual arithmetic operators:
-the binary <code>+</code> (addition),
-<code>-</code> (subtraction), <code>*</code> (multiplication),
-<code>/</code> (division), <code>%</code> (modulo), and <code>^</code> (exponentiation);
-and unary <code>-</code> (negation).
-If the operands are numbers, or strings that can be converted to
-numbers (see <a href="#2.2.1">&sect;2.2.1</a>),
-then all operations have the usual meaning.
-Exponentiation works for any exponent.
-For instance, <code>x^(-0.5)</code> computes the inverse of the square root of <code>x</code>.
-Modulo is defined as
-<pre>
-     a % b == a - math.floor(a/b)*b
-</pre><p>
-That is, it is the remainder of a division that rounds
-the quotient towards minus infinity.
-<h3>2.5.2 - <a name="2.5.2">Relational Operators</a></h3><p>
-The relational operators in Lua are
-<pre>
-     ==    ~=    &lt;     &gt;     &lt;=    &gt;=
-</pre><p>
-These operators always result in <b>false</b> or <b>true</b>.
-<p>
-Equality (<code>==</code>) first compares the type of its operands.
-If the types are different, then the result is <b>false</b>.
-Otherwise, the values of the operands are compared.
-Numbers and strings are compared in the usual way.
-Objects (tables, userdata, threads, and functions)
-are compared by <em>reference</em>:
-two objects are considered equal only if they are the <em>same</em> object.
-Every time you create a new object
-(a table, userdata, thread, or function),
-this new object is different from any previously existing object.
-<p>
-You can change the way that Lua compares tables and userdata 
-by using the "eq" metamethod (see <a href="#2.8">&sect;2.8</a>).
-<p>
-The conversion rules of <a href="#2.2.1">&sect;2.2.1</a>
-<em>do not</em> apply to equality comparisons.
-Thus, <code>"0"==0</code> evaluates to <b>false</b>,
-and <code>t[0]</code> and <code>t["0"]</code> denote different
-entries in a table.
-<p>
-The operator <code>~=</code> is exactly the negation of equality (<code>==</code>).
-<p>
-The order operators work as follows.
-If both arguments are numbers, then they are compared as such.
-Otherwise, if both arguments are strings,
-then their values are compared according to the current locale.
-Otherwise, Lua tries to call the "lt" or the "le"
-metamethod (see <a href="#2.8">&sect;2.8</a>).
-A comparison <code>a &gt; b</code> is translated to <code>b &lt; a</code>
-and <code>a &gt;= b</code> is translated to <code>b &lt;= a</code>.
-<h3>2.5.3 - <a name="2.5.3">Logical Operators</a></h3><p>
-The logical operators in Lua are
-<b>and</b>, <b>or</b>, and <b>not</b>.
-Like the control structures (see <a href="#2.4.4">&sect;2.4.4</a>),
-all logical operators consider both <b>false</b> and <b>nil</b> as false
-and anything else as true.
-<p>
-The negation operator <b>not</b> always returns <b>false</b> or <b>true</b>.
-The conjunction operator <b>and</b> returns its first argument
-if this value is <b>false</b> or <b>nil</b>;
-otherwise, <b>and</b> returns its second argument.
-The disjunction operator <b>or</b> returns its first argument
-if this value is different from <b>nil</b> and <b>false</b>;
-otherwise, <b>or</b> returns its second argument.
-Both <b>and</b> and <b>or</b> use short-cut evaluation;
-that is,
-the second operand is evaluated only if necessary.
-Here are some examples:
-<pre>
-     10 or 20            --&gt; 10
-     10 or error()       --&gt; 10
-     nil or "a"          --&gt; "a"
-     nil and 10          --&gt; nil
-     false and error()   --&gt; false
-     false and nil       --&gt; false
-     false or nil        --&gt; nil
-     10 and 20           --&gt; 20
-</pre><p>
-(In this manual,
-<code>--&gt;</code> indicates the result of the preceding expression.)
-<h3>2.5.4 - <a name="2.5.4">Concatenation</a></h3><p>
-The string concatenation operator in Lua is
-denoted by two dots ('<code>..</code>').
-If both operands are strings or numbers, then they are converted to
-strings according to the rules mentioned in <a href="#2.2.1">&sect;2.2.1</a>.
-Otherwise, the "concat" metamethod is called (see <a href="#2.8">&sect;2.8</a>).
-<h3>2.5.5 - <a name="2.5.5">The Length Operator</a></h3>
-<p>
-The length operator is denoted by the unary operator <code>#</code>.
-The length of a string is its number of bytes
-(that is, the usual meaning of string length when each
-character is one byte).
-<p>
-The length of a table <code>t</code> is defined to be any
-integer index <code>n</code>
-such that <code>t[n]</code> is not <b>nil</b> and <code>t[n+1]</code> is <b>nil</b>;
-moreover, if <code>t[1]</code> is <b>nil</b>, <code>n</code> can be zero.
-For a regular array, with non-nil values from 1 to a given <code>n</code>,
-its length is exactly that <code>n</code>,
-the index of its last value.
-If the array has "holes"
-(that is, <b>nil</b> values between other non-nil values),
-then <code>#t</code> can be any of the indices that
-directly precedes a <b>nil</b> value
-(that is, it may consider any such <b>nil</b> value as the end of
-the array). 
-<h3>2.5.6 - <a name="2.5.6">Precedence</a></h3><p>
-Operator precedence in Lua follows the table below,
-from lower to higher priority:
-<pre>
-     or
-     and
-     &lt;     &gt;     &lt;=    &gt;=    ~=    ==
-     ..
-     +     -
-     *     /     %
-     not   #     - (unary)
-     ^
-</pre><p>
-As usual,
-you can use parentheses to change the precedences of an expression.
-The concatenation ('<code>..</code>') and exponentiation ('<code>^</code>')
-operators are right associative.
-All other binary operators are left associative.
-<h3>2.5.7 - <a name="2.5.7">Table Constructors</a></h3><p>
-Table constructors are expressions that create tables.
-Every time a constructor is evaluated, a new table is created.
-A constructor can be used to create an empty table
-or to create a table and initialize some of its fields.
-The general syntax for constructors is
-<pre>
-        tableconstructor ::= `<b>{</b>&acute; [fieldlist] `<b>}</b>&acute;
-        fieldlist ::= field {fieldsep field} [fieldsep]
-        field ::= `<b>[</b>&acute; exp `<b>]</b>&acute; `<b>=</b>&acute; exp | Name `<b>=</b>&acute; exp | exp
-        fieldsep ::= `<b>,</b>&acute; | `<b>;</b>&acute;
-</pre>
-<p>
-Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry
-with key <code>exp1</code> and value <code>exp2</code>.
-A field of the form <code>name = exp</code> is equivalent to
-<code>["name"] = exp</code>.
-Finally, fields of the form <code>exp</code> are equivalent to
-<code>[i] = exp</code>, where <code>i</code> are consecutive numerical integers,
-starting with 1.
-Fields in the other formats do not affect this counting.
-For example,
-<pre>
-     a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }
-</pre><p>
-is equivalent to
-<pre>
-     do
-       local t = {}
-       t[f(1)] = g
-       t[1] = "x"         -- 1st exp
-       t[2] = "y"         -- 2nd exp
-       t.x = 1            -- t["x"] = 1
-       t[3] = f(x)        -- 3rd exp
-       t[30] = 23
-       t[4] = 45          -- 4th exp
-       a = t
-     end
-</pre>
-<p>
-If the last field in the list has the form <code>exp</code>
-and the expression is a function call or a vararg expression,
-then all values returned by this expression enter the list consecutively
-(see <a href="#2.5.8">&sect;2.5.8</a>).
-To avoid this,
-enclose the function call or the vararg expression
-in parentheses (see <a href="#2.5">&sect;2.5</a>).
-<p>
-The field list can have an optional trailing separator,
-as a convenience for machine-generated code.
-<h3>2.5.8 - <a name="2.5.8">Function Calls</a></h3><p>
-A function call in Lua has the following syntax:
-<pre>
-        functioncall ::= prefixexp args
-</pre><p>
-In a function call,
-first prefixexp and args are evaluated.
-If the value of prefixexp has type <em>function</em>,
-then this function is called
-with the given arguments.
-Otherwise, the prefixexp "call" metamethod is called,
-having as first parameter the value of prefixexp,
-followed by the original call arguments
-(see <a href="#2.8">&sect;2.8</a>).
-<p>
-The form
-<pre>
-        functioncall ::= prefixexp `<b>:</b>&acute; Name args
-</pre><p>
-can be used to call "methods".
-A call <code>v:name(<em>args</em>)</code>
-is syntactic sugar for <code>v.name(v,<em>args</em>)</code>,
-except that <code>v</code> is evaluated only once.
-<p>
-Arguments have the following syntax:
-<pre>
-        args ::= `<b>(</b>&acute; [explist] `<b>)</b>&acute;
-        args ::= tableconstructor
-        args ::= String
-</pre><p>
-All argument expressions are evaluated before the call.
-A call of the form <code>f{<em>fields</em>}</code> is
-syntactic sugar for <code>f({<em>fields</em>})</code>;
-that is, the argument list is a single new table.
-A call of the form <code>f'<em>string</em>'</code>
-(or <code>f"<em>string</em>"</code> or <code>f[[<em>string</em>]]</code>)
-is syntactic sugar for <code>f('<em>string</em>')</code>;
-that is, the argument list is a single literal string.
-<p>
-As an exception to the free-format syntax of Lua,
-you cannot put a line break before the '<code>(</code>' in a function call.
-This restriction avoids some ambiguities in the language.
-If you write
-<pre>
-     a = f
-     (g).x(a)
-</pre><p>
-Lua would see that as a single statement, <code>a = f(g).x(a)</code>.
-So, if you want two statements, you must add a semi-colon between them.
-If you actually want to call <code>f</code>,
-you must remove the line break before <code>(g)</code>.
-<p>
-A call of the form <code>return</code> <em>functioncall</em> is called
-a <em>tail call</em>.
-Lua implements <em>proper tail calls</em>
-(or <em>proper tail recursion</em>):
-in a tail call,
-the called function reuses the stack entry of the calling function.
-Therefore, there is no limit on the number of nested tail calls that
-a program can execute.
-However, a tail call erases any debug information about the
-calling function.
-Note that a tail call only happens with a particular syntax,
-where the <b>return</b> has one single function call as argument;
-this syntax makes the calling function return exactly
-the returns of the called function.
-So, none of the following examples are tail calls:
-<pre>
-     return (f(x))        -- results adjusted to 1
-     return 2 * f(x)
-     return x, f(x)       -- additional results
-     f(x); return         -- results discarded
-     return x or f(x)     -- results adjusted to 1
-</pre>
-<h3>2.5.9 - <a name="2.5.9">Function Definitions</a></h3>
-<p>
-The syntax for function definition is
-<pre>
-        function ::= <b>function</b> funcbody
-        funcbody ::= `<b>(</b>&acute; [parlist] `<b>)</b>&acute; block <b>end</b>
-</pre>
-<p>
-The following syntactic sugar simplifies function definitions:
-<pre>
-        stat ::= <b>function</b> funcname funcbody
-        stat ::= <b>local</b> <b>function</b> Name funcbody
-        funcname ::= Name {`<b>.</b>&acute; Name} [`<b>:</b>&acute; Name]
-</pre><p>
-The statement
-<pre>
-     function f () <em>body</em> end
-</pre><p>
-translates to
-<pre>
-     f = function () <em>body</em> end
-</pre><p>
-The statement
-<pre>
-     function t.a.b.c.f () <em>body</em> end
-</pre><p>
-translates to
-<pre>
-     t.a.b.c.f = function () <em>body</em> end
-</pre><p>
-The statement
-<pre>
-     local function f () <em>body</em> end
-</pre><p>
-translates to
-<pre>
-     local f; f = function () <em>body</em> end
-</pre><p>
-<em>not</em> to
-<pre>
-     local f = function () <em>body</em> end
-</pre><p>
-(This only makes a difference when the body of the function
-contains references to <code>f</code>.)
-<p>
-A function definition is an executable expression,
-whose value has type <em>function</em>.
-When Lua pre-compiles a chunk,
-all its function bodies are pre-compiled too.
-Then, whenever Lua executes the function definition,
-the function is <em>instantiated</em> (or <em>closed</em>).
-This function instance (or <em>closure</em>)
-is the final value of the expression.
-Different instances of the same function
-can refer to different  external local variables
-and can have different environment tables.
-<p>
-Parameters act as local variables that are
-initialized with the argument values:
-<pre>
-        parlist ::= namelist [`<b>,</b>&acute; `<b>...</b>&acute;] | `<b>...</b>&acute;
-</pre><p>
-When a function is called,
-the list of arguments is adjusted to
-the length of the list of parameters,
-unless the function is a variadic or <em>vararg function</em>,
-which is
-indicated by three dots ('<code>...</code>') at the end of its parameter list.
-A vararg function does not adjust its argument list;
-instead, it collects all extra arguments and supplies them
-to the function through a <em>vararg expression</em>,
-which is also written as three dots.
-The value of this expression is a list of all actual extra arguments,
-similar to a function with multiple results.
-If a vararg expression is used inside another expression
-or in the middle of a list of expressions,
-then its return list is adjusted to one element.
-If the expression is used as the last element of a list of expressions,
-then no adjustment is made
-(unless that last expression is enclosed in parentheses).
-<p>
-As an example, consider the following definitions:
-<pre>
-     function f(a, b) end
-     function g(a, b, ...) end
-     function r() return 1,2,3 end
-</pre><p>
-Then, we have the following mapping from arguments to parameters and
-to the vararg expression:
-<pre>
-     CALL            PARAMETERS
-     
-     f(3)             a=3, b=nil
-     f(3, 4)          a=3, b=4
-     f(3, 4, 5)       a=3, b=4
-     f(r(), 10)       a=1, b=10
-     f(r())           a=1, b=2
-     
-     g(3)             a=3, b=nil, ... --&gt;  (nothing)
-     g(3, 4)          a=3, b=4,   ... --&gt;  (nothing)
-     g(3, 4, 5, 8)    a=3, b=4,   ... --&gt;  5  8
-     g(5, r())        a=5, b=1,   ... --&gt;  2  3
-</pre>
-<p>
-Results are returned using the <b>return</b> statement (see <a href="#2.4.4">&sect;2.4.4</a>).
-If control reaches the end of a function
-without encountering a <b>return</b> statement,
-then the function returns with no results.
-<p>
-The <em>colon</em> syntax
-is used for defining <em>methods</em>,
-that is, functions that have an implicit extra parameter <code>self</code>.
-Thus, the statement
-<pre>
-     function t.a.b.c:f (<em>params</em>) <em>body</em> end
-</pre><p>
-is syntactic sugar for
-<pre>
-     t.a.b.c.f = function (self, <em>params</em>) <em>body</em> end
-</pre>
-<h2>2.6 - <a name="2.6">Visibility Rules</a></h2>
-<p>
-Lua is a lexically scoped language.
-The scope of variables begins at the first statement <em>after</em>
-their declaration and lasts until the end of the innermost block that
-includes the declaration.
-Consider the following example:
-<pre>
-     x = 10                -- global variable
-     do                    -- new block
-       local x = x         -- new 'x', with value 10
-       print(x)            --&gt; 10
-       x = x+1
-       do                  -- another block
-         local x = x+1     -- another 'x'
-         print(x)          --&gt; 12
-       end
-       print(x)            --&gt; 11
-     end
-     print(x)              --&gt; 10  (the global one)
-</pre>
-<p>
-Notice that, in a declaration like <code>local x = x</code>,
-the new <code>x</code> being declared is not in scope yet,
-and so the second <code>x</code> refers to the outside variable.
-<p>
-Because of the lexical scoping rules,
-local variables can be freely accessed by functions
-defined inside their scope.
-A local variable used by an inner function is called
-an <em>upvalue</em>, or <em>external local variable</em>,
-inside the inner function.
-<p>
-Notice that each execution of a <b>local</b> statement
-defines new local variables.
-Consider the following example:
-<pre>
-     a = {}
-     local x = 20
-     for i=1,10 do
-       local y = 0
-       a[i] = function () y=y+1; return x+y end
-     end
-</pre><p>
-The loop creates ten closures
-(that is, ten instances of the anonymous function).
-Each of these closures uses a different <code>y</code> variable,
-while all of them share the same <code>x</code>.
-<h2>2.7 - <a name="2.7">Error Handling</a></h2>
-<p>
-Because Lua is an embedded extension language,
-all Lua actions start from C&nbsp;code in the host program
-calling a function from the Lua library (see <a href="#lua_pcall"><code>lua_pcall</code></a>).
-Whenever an error occurs during Lua compilation or execution,
-control returns to C,
-which can take appropriate measures
-(such as printing an error message).
-<p>
-Lua code can explicitly generate an error by calling the
-<a href="#pdf-error"><code>error</code></a> function.
-If you need to catch errors in Lua,
-you can use the <a href="#pdf-pcall"><code>pcall</code></a> function.
-<h2>2.8 - <a name="2.8">Metatables</a></h2>
-<p>
-Every value in Lua can have a <em>metatable</em>.
-This <em>metatable</em> is an ordinary Lua table
-that defines the behavior of the original value
-under certain special operations.
-You can change several aspects of the behavior
-of operations over a value by setting specific fields in its metatable.
-For instance, when a non-numeric value is the operand of an addition,
-Lua checks for a function in the field <code>"__add"</code> in its metatable.
-If it finds one,
-Lua calls this function to perform the addition.
-<p>
-We call the keys in a metatable <em>events</em>
-and the values <em>metamethods</em>.
-In the previous example, the event is <code>"add"</code> 
-and the metamethod is the function that performs the addition.
-<p>
-You can query the metatable of any value
-through the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function.
-<p>
-You can replace the metatable of tables
-through the <a href="#pdf-setmetatable"><code>setmetatable</code></a>
-function.
-You cannot change the metatable of other types from Lua
-(except by using the debug library);
-you must use the C&nbsp;API for that.
-<p>
-Tables and full userdata have individual metatables
-(although multiple tables and userdata can share their metatables).
-Values of all other types share one single metatable per type;
-that is, there is one single metatable for all numbers,
-one for all strings, etc.
-<p>
-A metatable controls how an object behaves in arithmetic operations,
-order comparisons, concatenation, length operation, and indexing.
-A metatable also can define a function to be called when a userdata
-is garbage collected.
-For each of these operations Lua associates a specific key
-called an <em>event</em>.
-When Lua performs one of these operations over a value,
-it checks whether this value has a metatable with the corresponding event.
-If so, the value associated with that key (the metamethod)
-controls how Lua will perform the operation.
-<p>
-Metatables control the operations listed next.
-Each operation is identified by its corresponding name.
-The key for each operation is a string with its name prefixed by
-two underscores, '<code>__</code>';
-for instance, the key for operation "add" is the
-string <code>"__add"</code>.
-The semantics of these operations is better explained by a Lua function
-describing how the interpreter executes the operation.
-<p>
-The code shown here in Lua is only illustrative;
-the real behavior is hard coded in the interpreter
-and it is much more efficient than this simulation.
-All functions used in these descriptions
-(<a href="#pdf-rawget"><code>rawget</code></a>, <a href="#pdf-tonumber"><code>tonumber</code></a>, etc.)
-are described in <a href="#5.1">&sect;5.1</a>.
-In particular, to retrieve the metamethod of a given object,
-we use the expression
-<pre>
-     metatable(obj)[event]
-</pre><p>
-This should be read as
-<pre>
-     rawget(getmetatable(obj) or {}, event)
-</pre><p>
-That is, the access to a metamethod does not invoke other metamethods,
-and the access to objects with no metatables does not fail
-(it simply results in <b>nil</b>).
-<ul>
-<li><b>"add":</b>
-the <code>+</code> operation.
-<p>
-The function <code>getbinhandler</code> below defines how Lua chooses a handler
-for a binary operation.
-First, Lua tries the first operand.
-If its type does not define a handler for the operation,
-then Lua tries the second operand.
-<pre>
-     function getbinhandler (op1, op2, event)
-       return metatable(op1)[event] or metatable(op2)[event]
-     end
-</pre><p>
-By using this function,
-the behavior of the <code>op1 + op2</code> is
-<pre>
-     function add_event (op1, op2)
-       local o1, o2 = tonumber(op1), tonumber(op2)
-       if o1 and o2 then  -- both operands are numeric?
-         return o1 + o2   -- '+' here is the primitive 'add'
-       else  -- at least one of the operands is not numeric
-         local h = getbinhandler(op1, op2, "__add")
-         if h then
-           -- call the handler with both operands
-           return (h(op1, op2))
-         else  -- no handler available: default behavior
-           error(&middot;&middot;&middot;)
-         end
-       end
-     end
-</pre><p>
-</li>
-<li><b>"sub":</b>
-the <code>-</code> operation.
-Behavior similar to the "add" operation.
-</li>
-<li><b>"mul":</b>
-the <code>*</code> operation.
-Behavior similar to the "add" operation.
-</li>
-<li><b>"div":</b>
-the <code>/</code> operation.
-Behavior similar to the "add" operation.
-</li>
-<li><b>"mod":</b>
-the <code>%</code> operation.
-Behavior similar to the "add" operation,
-with the operation
-<code>o1 - floor(o1/o2)*o2</code> as the primitive operation.
-</li>
-<li><b>"pow":</b>
-the <code>^</code> (exponentiation) operation.
-Behavior similar to the "add" operation,
-with the function <code>pow</code> (from the C&nbsp;math library)
-as the primitive operation.
-</li>
-<li><b>"unm":</b>
-the unary <code>-</code> operation.
-<pre>
-     function unm_event (op)
-       local o = tonumber(op)
-       if o then  -- operand is numeric?
-         return -o  -- '-' here is the primitive 'unm'
-       else  -- the operand is not numeric.
-         -- Try to get a handler from the operand
-         local h = metatable(op).__unm
-         if h then
-           -- call the handler with the operand
-           return (h(op))
-         else  -- no handler available: default behavior
-           error(&middot;&middot;&middot;)
-         end
-       end
-     end
-</pre><p>
-</li>
-<li><b>"concat":</b>
-the <code>..</code> (concatenation) operation.
-<pre>
-     function concat_event (op1, op2)
-       if (type(op1) == "string" or type(op1) == "number") and
-          (type(op2) == "string" or type(op2) == "number") then
-         return op1 .. op2  -- primitive string concatenation
-       else
-         local h = getbinhandler(op1, op2, "__concat")
-         if h then
-           return (h(op1, op2))
-         else
-           error(&middot;&middot;&middot;)
-         end
-       end
-     end
-</pre><p>
-</li>
-<li><b>"len":</b>
-the <code>#</code> operation.
-<pre>
-     function len_event (op)
-       if type(op) == "string" then
-         return strlen(op)         -- primitive string length
-       elseif type(op) == "table" then
-         return #op                -- primitive table length
-       else
-         local h = metatable(op).__len
-         if h then
-           -- call the handler with the operand
-           return (h(op))
-         else  -- no handler available: default behavior
-           error(&middot;&middot;&middot;)
-         end
-       end
-     end
-</pre><p>
-See <a href="#2.5.5">&sect;2.5.5</a> for a description of the length of a table.
-</li>
-<li><b>"eq":</b>
-the <code>==</code> operation.
-The function <code>getcomphandler</code> defines how Lua chooses a metamethod
-for comparison operators.
-A metamethod only is selected when both objects
-being compared have the same type
-and the same metamethod for the selected operation.
-<pre>
-     function getcomphandler (op1, op2, event)
-       if type(op1) ~= type(op2) then return nil end
-       local mm1 = metatable(op1)[event]
-       local mm2 = metatable(op2)[event]
-       if mm1 == mm2 then return mm1 else return nil end
-     end
-</pre><p>
-The "eq" event is defined as follows:
-<pre>
-     function eq_event (op1, op2)
-       if type(op1) ~= type(op2) then  -- different types?
-         return false   -- different objects
-       end
-       if op1 == op2 then   -- primitive equal?
-         return true   -- objects are equal
-       end
-       -- try metamethod
-       local h = getcomphandler(op1, op2, "__eq")
-       if h then
-         return (h(op1, op2))
-       else
-         return false
-       end
-     end
-</pre><p>
-<code>a ~= b</code> is equivalent to <code>not (a == b)</code>.
-</li>
-<li><b>"lt":</b>
-the <code>&lt;</code> operation.
-<pre>
-     function lt_event (op1, op2)
-       if type(op1) == "number" and type(op2) == "number" then
-         return op1 &lt; op2   -- numeric comparison
-       elseif type(op1) == "string" and type(op2) == "string" then
-         return op1 &lt; op2   -- lexicographic comparison
-       else
-         local h = getcomphandler(op1, op2, "__lt")
-         if h then
-           return (h(op1, op2))
-         else
-           error(&middot;&middot;&middot;)
-         end
-       end
-     end
-</pre><p>
-<code>a &gt; b</code> is equivalent to <code>b &lt; a</code>.
-</li>
-<li><b>"le":</b>
-the <code>&lt;=</code> operation.
-<pre>
-     function le_event (op1, op2)
-       if type(op1) == "number" and type(op2) == "number" then
-         return op1 &lt;= op2   -- numeric comparison
-       elseif type(op1) == "string" and type(op2) == "string" then
-         return op1 &lt;= op2   -- lexicographic comparison
-       else
-         local h = getcomphandler(op1, op2, "__le")
-         if h then
-           return (h(op1, op2))
-         else
-           h = getcomphandler(op1, op2, "__lt")
-           if h then
-             return not h(op2, op1)
-           else
-             error(&middot;&middot;&middot;)
-           end
-         end
-       end
-     end
-</pre><p>
-<code>a &gt;= b</code> is equivalent to <code>b &lt;= a</code>.
-Note that, in the absence of a "le" metamethod,
-Lua tries the "lt", assuming that <code>a &lt;= b</code> is
-equivalent to <code>not (b &lt; a)</code>.
-</li>
-<li><b>"index":</b>
-The indexing access <code>table[key]</code>.
-<pre>
-     function gettable_event (table, key)
-       local h
-       if type(table) == "table" then
-         local v = rawget(table, key)
-         if v ~= nil then return v end
-         h = metatable(table).__index
-         if h == nil then return nil end
-       else
-         h = metatable(table).__index
-         if h == nil then
-           error(&middot;&middot;&middot;)
-         end
-       end
-       if type(h) == "function" then
-         return (h(table, key))     -- call the handler
-       else return h[key]           -- or repeat operation on it
-       end
-     end
-</pre><p>
-</li>
-<li><b>"newindex":</b>
-The indexing assignment <code>table[key] = value</code>.
-<pre>
-     function settable_event (table, key, value)
-       local h
-       if type(table) == "table" then
-         local v = rawget(table, key)
-         if v ~= nil then rawset(table, key, value); return end
-         h = metatable(table).__newindex
-         if h == nil then rawset(table, key, value); return end
-       else
-         h = metatable(table).__newindex
-         if h == nil then
-           error(&middot;&middot;&middot;)
-         end
-       end
-       if type(h) == "function" then
-         h(table, key,value)           -- call the handler
-       else h[key] = value             -- or repeat operation on it
-       end
-     end
-</pre><p>
-</li>
-<li><b>"call":</b>
-called when Lua calls a value.
-<pre>
-     function function_event (func, ...)
-       if type(func) == "function" then
-         return func(...)   -- primitive call
-       else
-         local h = metatable(func).__call
-         if h then
-           return h(func, ...)
-         else
-           error(&middot;&middot;&middot;)
-         end
-       end
-     end
-</pre><p>
-</li>
-</ul>
-<h2>2.9 - <a name="2.9">Environments</a></h2>
-<p>
-Besides metatables,
-objects of types thread, function, and userdata
-have another table associated with them,
-called their <em>environment</em>.
-Like metatables, environments are regular tables and
-multiple objects can share the same environment.
-<p>
-Threads are created sharing the environment of the creating thread.
-Userdata and C&nbsp;functions are created sharing the environment
-of the creating C&nbsp;function.
-Non-nested Lua functions
-(created by <a href="#pdf-loadfile"><code>loadfile</code></a>, <a href="#pdf-loadstring"><code>loadstring</code></a> or <a href="#pdf-load"><code>load</code></a>)
-are created sharing the environment of the creating thread.
-Nested Lua functions are created sharing the environment of
-the creating Lua function.
-<p>
-Environments associated with userdata have no meaning for Lua.
-It is only a convenience feature for programmers to associate a table to
-a userdata.
-<p>
-Environments associated with threads are called
-<em>global environments</em>.
-They are used as the default environment for threads and
-non-nested Lua functions created by the thread
-and can be directly accessed by C&nbsp;code (see <a href="#3.3">&sect;3.3</a>).
-<p>
-The environment associated with a C&nbsp;function can be directly
-accessed by C&nbsp;code (see <a href="#3.3">&sect;3.3</a>).
-It is used as the default environment for other C&nbsp;functions
-and userdata created by the function.
-<p>
-Environments associated with Lua functions are used to resolve
-all accesses to global variables within the function (see <a href="#2.3">&sect;2.3</a>).
-They are used as the default environment for nested Lua functions
-created by the function.
-<p>
-You can change the environment of a Lua function or the
-running thread by calling <a href="#pdf-setfenv"><code>setfenv</code></a>.
-You can get the environment of a Lua function or the running thread
-by calling <a href="#pdf-getfenv"><code>getfenv</code></a>.
-To manipulate the environment of other objects
-(userdata, C&nbsp;functions, other threads) you must
-use the C&nbsp;API.
-<h2>2.10 - <a name="2.10">Garbage Collection</a></h2>
-<p>
-Lua performs automatic memory management.
-This means that
-you have to worry neither about allocating memory for new objects
-nor about freeing it when the objects are no longer needed.
-Lua manages memory automatically by running
-a <em>garbage collector</em> from time to time
-to collect all <em>dead objects</em>
-(that is, objects that are no longer accessible from Lua).
-All memory used by Lua is subject to automatic management:
-tables, userdata, functions, threads, strings, etc.
-<p>
-Lua implements an incremental mark-and-sweep collector.
-It uses two numbers to control its garbage-collection cycles:
-the <em>garbage-collector pause</em> and
-the <em>garbage-collector step multiplier</em>.
-Both use percentage points as units
-(so that a value of 100 means an internal value of 1).
-<p>
-The garbage-collector pause
-controls how long the collector waits before starting a new cycle.
-Larger values make the collector less aggressive.
-Values smaller than 100 mean the collector will not wait to
-start a new cycle.
-A value of 200 means that the collector waits for the total memory in use
-to double before starting a new cycle.
-<p>
-The step multiplier
-controls the relative speed of the collector relative to
-memory allocation.
-Larger values make the collector more aggressive but also increase
-the size of each incremental step.
-Values smaller than 100 make the collector too slow and
-can result in the collector never finishing a cycle.
-The default, 200, means that the collector runs at "twice"
-the speed of memory allocation.
-<p>
-You can change these numbers by calling <a href="#lua_gc"><code>lua_gc</code></a> in C
-or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua.
-With these functions you can also control 
-the collector directly (e.g., stop and restart it).
-<h3>2.10.1 - <a name="2.10.1">Garbage-Collection Metamethods</a></h3>
-<p>
-Using the C&nbsp;API,
-you can set garbage-collector metamethods for userdata (see <a href="#2.8">&sect;2.8</a>).
-These metamethods are also called <em>finalizers</em>.
-Finalizers allow you to coordinate Lua's garbage collection
-with external resource management
-(such as closing files, network or database connections,
-or freeing your own memory).
-<p>
-Garbage userdata with a field <code>__gc</code> in their metatables are not
-collected immediately by the garbage collector.
-Instead, Lua puts them in a list.
-After the collection,
-Lua does the equivalent of the following function
-for each userdata in that list:
-<pre>
-     function gc_event (udata)
-       local h = metatable(udata).__gc
-       if h then
-         h(udata)
-       end
-     end
-</pre>
-<p>
-At the end of each garbage-collection cycle,
-the finalizers for userdata are called in <em>reverse</em>
-order of their creation,
-among those collected in that cycle.
-That is, the first finalizer to be called is the one associated
-with the userdata created last in the program.
-The userdata itself is freed only in the next garbage-collection cycle.
-<h3>2.10.2 - <a name="2.10.2">Weak Tables</a></h3>
-<p>
-A <em>weak table</em> is a table whose elements are
-<em>weak references</em>.
-A weak reference is ignored by the garbage collector.
-In other words,
-if the only references to an object are weak references,
-then the garbage collector will collect this object.
-<p>
-A weak table can have weak keys, weak values, or both.
-A table with weak keys allows the collection of its keys,
-but prevents the collection of its values.
-A table with both weak keys and weak values allows the collection of
-both keys and values.
-In any case, if either the key or the value is collected,
-the whole pair is removed from the table.
-The weakness of a table is controlled by the
-<code>__mode</code> field of its metatable.
-If the <code>__mode</code> field is a string containing the character&nbsp;'<code>k</code>',
-the keys in the table are weak.
-If <code>__mode</code> contains '<code>v</code>',
-the values in the table are weak.
-<p>
-After you use a table as a metatable,
-you should not change the value of its <code>__mode</code> field.
-Otherwise, the weak behavior of the tables controlled by this
-metatable is undefined.
-<h2>2.11 - <a name="2.11">Coroutines</a></h2>
-<p>
-Lua supports coroutines,
-also called <em>collaborative multithreading</em>.
-A coroutine in Lua represents an independent thread of execution.
-Unlike threads in multithread systems, however,
-a coroutine only suspends its execution by explicitly calling
-a yield function.
-<p>
-You create a coroutine with a call to <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>.
-Its sole argument is a function
-that is the main function of the coroutine.
-The <code>create</code> function only creates a new coroutine and
-returns a handle to it (an object of type <em>thread</em>);
-it does not start the coroutine execution.
-<p>
-When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
-passing as its first argument
-a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
-the coroutine starts its execution,
-at the first line of its main function.
-Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed on
-to the coroutine main function.
-After the coroutine starts running,
-it runs until it terminates or <em>yields</em>.
-<p>
-A coroutine can terminate its execution in two ways:
-normally, when its main function returns
-(explicitly or implicitly, after the last instruction);
-and abnormally, if there is an unprotected error.
-In the first case, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>,
-plus any values returned by the coroutine main function.
-In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b>
-plus an error message.
-<p>
-A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
-When a coroutine yields,
-the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately,
-even if the yield happens inside nested function calls
-(that is, not in the main function,
-but in a function directly or indirectly called by the main function).
-In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>,
-plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
-The next time you resume the same coroutine,
-it continues its execution from the point where it yielded,
-with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra
-arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
-<p>
-Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
-the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine,
-but instead of returning the coroutine itself,
-it returns a function that, when called, resumes the coroutine.
-Any arguments passed to this function
-go as extra arguments to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
-<a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
-except the first one (the boolean error code).
-Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
-<a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> does not catch errors;
-any error is propagated to the caller.
-<p>
-As an example,
-consider the following code:
-<pre>
-     function foo (a)
-       print("foo", a)
-       return coroutine.yield(2*a)
-     end
-     
-     co = coroutine.create(function (a,b)
-           print("co-body", a, b)
-           local r = foo(a+1)
-           print("co-body", r)
-           local r, s = coroutine.yield(a+b, a-b)
-           print("co-body", r, s)
-           return b, "end"
-     end)
-            
-     print("main", coroutine.resume(co, 1, 10))
-     print("main", coroutine.resume(co, "r"))
-     print("main", coroutine.resume(co, "x", "y"))
-     print("main", coroutine.resume(co, "x", "y"))
-</pre><p>
-When you run it, it produces the following output:
-<pre>
-     co-body 1       10
-     foo     2
-     
-     main    true    4
-     co-body r
-     main    true    11      -9
-     co-body x       y
-     main    true    10      end
-     main    false   cannot resume dead coroutine
-</pre>
-<h1>3 - <a name="3">The Application Program Interface</a></h1>
-<p>
-This section describes the C&nbsp;API for Lua, that is,
-the set of C&nbsp;functions available to the host program to communicate
-with Lua.
-All API functions and related types and constants
-are declared in the header file <a name="pdf-lua.h"><code>lua.h</code></a>.
-<p>
-Even when we use the term "function",
-any facility in the API may be provided as a macro instead.
-All such macros use each of their arguments exactly once
-(except for the first argument, which is always a Lua state),
-and so do not generate any hidden side-effects.
-<p>
-As in most C&nbsp;libraries,
-the Lua API functions do not check their arguments for validity or consistency.
-However, you can change this behavior by compiling Lua
-with a proper definition for the macro <a name="pdf-luai_apicheck"><code>luai_apicheck</code></a>,
-in file <code>luaconf.h</code>.
-<h2>3.1 - <a name="3.1">The Stack</a></h2>
-<p>
-Lua uses a <em>virtual stack</em> to pass values to and from C.
-Each element in this stack represents a Lua value
-(<b>nil</b>, number, string, etc.).
-<p>
-Whenever Lua calls C, the called function gets a new stack,
-which is independent of previous stacks and of stacks of
-C&nbsp;functions that are still active.
-This stack initially contains any arguments to the C&nbsp;function
-and it is where the C&nbsp;function pushes its results
-to be returned to the caller (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
-<p>
-For convenience,
-most query operations in the API do not follow a strict stack discipline.
-Instead, they can refer to any element in the stack
-by using an <em>index</em>:
-A positive index represents an <em>absolute</em> stack position
-(starting at&nbsp;1);
-a negative index represents an <em>offset</em> relative to the top of the stack.
-More specifically, if the stack has <em>n</em> elements,
-then index&nbsp;1 represents the first element
-(that is, the element that was pushed onto the stack first)
-and
-index&nbsp;<em>n</em> represents the last element;
-index&nbsp;-1 also represents the last element
-(that is, the element at the&nbsp;top)
-and index <em>-n</em> represents the first element.
-We say that an index is <em>valid</em>
-if it lies between&nbsp;1 and the stack top
-(that is, if <code>1 &le; abs(index) &le; top</code>).
- 
-<h2>3.2 - <a name="3.2">Stack Size</a></h2>
-<p>
-When you interact with Lua API,
-you are responsible for ensuring consistency.
-In particular,
-<em>you are responsible for controlling stack overflow</em>.
-You can use the function <a href="#lua_checkstack"><code>lua_checkstack</code></a>
-to grow the stack size.
-<p>
-Whenever Lua calls C,
-it ensures that at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> stack positions are available.
-<code>LUA_MINSTACK</code> is defined as 20,
-so that usually you do not have to worry about stack space
-unless your code has loops pushing elements onto the stack.
-<p>
-Most query functions accept as indices any value inside the
-available stack space, that is, indices up to the maximum stack size
-you have set through <a href="#lua_checkstack"><code>lua_checkstack</code></a>.
-Such indices are called <em>acceptable indices</em>.
-More formally, we define an <em>acceptable index</em>
-as follows:
-<pre>
-     (index &lt; 0 &amp;&amp; abs(index) &lt;= top) ||
-     (index &gt; 0 &amp;&amp; index &lt;= stackspace)
-</pre><p>
-Note that 0 is never an acceptable index.
-<h2>3.3 - <a name="3.3">Pseudo-Indices</a></h2>
-<p>
-Unless otherwise noted,
-any function that accepts valid indices can also be called with
-<em>pseudo-indices</em>,
-which represent some Lua values that are accessible to C&nbsp;code
-but which are not in the stack.
-Pseudo-indices are used to access the thread environment,
-the function environment,
-the registry,
-and the upvalues of a C&nbsp;function (see <a href="#3.4">&sect;3.4</a>).
-<p>
-The thread environment (where global variables live) is
-always at pseudo-index <a name="pdf-LUA_GLOBALSINDEX"><code>LUA_GLOBALSINDEX</code></a>.
-The environment of the running C&nbsp;function is always
-at pseudo-index <a name="pdf-LUA_ENVIRONINDEX"><code>LUA_ENVIRONINDEX</code></a>.
-<p>
-To access and change the value of global variables,
-you can use regular table operations over an environment table.
-For instance, to access the value of a global variable, do
-<pre>
-     lua_getfield(L, LUA_GLOBALSINDEX, varname);
-</pre>
-<h2>3.4 - <a name="3.4">C Closures</a></h2>
-<p>
-When a C&nbsp;function is created,
-it is possible to associate some values with it,
-thus creating a <em>C&nbsp;closure</em>;
-these values are called <em>upvalues</em> and are
-accessible to the function whenever it is called
-(see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>).
-<p>
-Whenever a C&nbsp;function is called,
-its upvalues are located at specific pseudo-indices.
-These pseudo-indices are produced by the macro
-<a name="lua_upvalueindex"><code>lua_upvalueindex</code></a>.
-The first value associated with a function is at position
-<code>lua_upvalueindex(1)</code>, and so on.
-Any access to <code>lua_upvalueindex(<em>n</em>)</code>,
-where <em>n</em> is greater than the number of upvalues of the
-current function (but not greater than 256),
-produces an acceptable (but invalid) index.
-<h2>3.5 - <a name="3.5">Registry</a></h2>
-<p>
-Lua provides a <em>registry</em>,
-a pre-defined table that can be used by any C&nbsp;code to
-store whatever Lua value it needs to store.
-This table is always located at pseudo-index
-<a name="pdf-LUA_REGISTRYINDEX"><code>LUA_REGISTRYINDEX</code></a>.
-Any C&nbsp;library can store data into this table,
-but it should take care to choose keys different from those used
-by other libraries, to avoid collisions.
-Typically, you should use as key a string containing your library name
-or a light userdata with the address of a C&nbsp;object in your code.
-<p>
-The integer keys in the registry are used by the reference mechanism,
-implemented by the auxiliary library,
-and therefore should not be used for other purposes.
-<h2>3.6 - <a name="3.6">Error Handling in C</a></h2>
-<p>
-Internally, Lua uses the C <code>longjmp</code> facility to handle errors.
-(You can also choose to use exceptions if you use C++;
-see file <code>luaconf.h</code>.)
-When Lua faces any error
-(such as memory allocation errors, type errors, syntax errors,
-and runtime errors)
-it <em>raises</em> an error;
-that is, it does a long jump.
-A <em>protected environment</em> uses <code>setjmp</code>
-to set a recover point;
-any error jumps to the most recent active recover point.
-<p>
-Most functions in the API can throw an error,
-for instance due to a memory allocation error.
-The documentation for each function indicates whether
-it can throw errors.
-<p>
-Inside a C&nbsp;function you can throw an error by calling <a href="#lua_error"><code>lua_error</code></a>.
-<h2>3.7 - <a name="3.7">Functions and Types</a></h2>
-<p>
-Here we list all functions and types from the C&nbsp;API in
-alphabetical order.
-Each function has an indicator like this:
-<span class="apii">[-o, +p, <em>x</em>]</span>
-<p>
-The first field, <code>o</code>,
-is how many elements the function pops from the stack.
-The second field, <code>p</code>,
-is how many elements the function pushes onto the stack.
-(Any function always pushes its results after popping its arguments.)
-A field in the form <code>x|y</code> means the function can push (or pop)
-<code>x</code> or <code>y</code> elements,
-depending on the situation;
-an interrogation mark '<code>?</code>' means that
-we cannot know how many elements the function pops/pushes
-by looking only at its arguments
-(e.g., they may depend on what is on the stack).
-The third field, <code>x</code>,
-tells whether the function may throw errors:
-'<code>-</code>' means the function never throws any error;
-'<code>m</code>' means the function may throw an error
-only due to not enough memory;
-'<code>e</code>' means the function may throw other kinds of errors;
-'<code>v</code>' means the function may throw an error on purpose.
-<hr><h3><a name="lua_Alloc"><code>lua_Alloc</code></a></h3>
-<pre>typedef void * (*lua_Alloc) (void *ud,
-                             void *ptr,
-                             size_t osize,
-                             size_t nsize);</pre>
-<p>
-The type of the memory-allocation function used by Lua states.
-The allocator function must provide a
-functionality similar to <code>realloc</code>,
-but not exactly the same.
-Its arguments are
-<code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>;
-<code>ptr</code>, a pointer to the block being allocated/reallocated/freed;
-<code>osize</code>, the original size of the block;
-<code>nsize</code>, the new size of the block.
-<code>ptr</code> is <code>NULL</code> if and only if <code>osize</code> is zero.
-When <code>nsize</code> is zero, the allocator must return <code>NULL</code>;
-if <code>osize</code> is not zero,
-it should free the block pointed to by <code>ptr</code>.
-When <code>nsize</code> is not zero, the allocator returns <code>NULL</code>
-if and only if it cannot fill the request.
-When <code>nsize</code> is not zero and <code>osize</code> is zero,
-the allocator should behave like <code>malloc</code>.
-When <code>nsize</code> and <code>osize</code> are not zero,
-the allocator behaves like <code>realloc</code>.
-Lua assumes that the allocator never fails when
-<code>osize &gt;= nsize</code>.
-<p>
-Here is a simple implementation for the allocator function.
-It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>.
-<pre>
-     static void *l_alloc (void *ud, void *ptr, size_t osize,
-                                                size_t nsize) {
-       (void)ud;  (void)osize;  /* not used */
-       if (nsize == 0) {
-         free(ptr);
-         return NULL;
-       }
-       else
-         return realloc(ptr, nsize);
-     }
-</pre><p>
-This code assumes
-that <code>free(NULL)</code> has no effect and that
-<code>realloc(NULL, size)</code> is equivalent to <code>malloc(size)</code>.
-ANSI&nbsp;C ensures both behaviors.
-<hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre>
-<p>
-Sets a new panic function and returns the old one.
-<p>
-If an error happens outside any protected environment,
-Lua calls a <em>panic function</em>
-and then calls <code>exit(EXIT_FAILURE)</code>,
-thus exiting the host application.
-Your panic function can avoid this exit by
-never returning (e.g., doing a long jump).
-<p>
-The panic function can access the error message at the top of the stack.
-<hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p>
-<span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span>
-<pre>void lua_call (lua_State *L, int nargs, int nresults);</pre>
-<p>
-Calls a function.
-<p>
-To call a function you must use the following protocol:
-first, the function to be called is pushed onto the stack;
-then, the arguments to the function are pushed
-in direct order;
-that is, the first argument is pushed first.
-Finally you call <a href="#lua_call"><code>lua_call</code></a>;
-<code>nargs</code> is the number of arguments that you pushed onto the stack.
-All arguments and the function value are popped from the stack
-when the function is called.
-The function results are pushed onto the stack when the function returns.
-The number of results is adjusted to <code>nresults</code>,
-unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>.
-In this case, <em>all</em> results from the function are pushed.
-Lua takes care that the returned values fit into the stack space.
-The function results are pushed onto the stack in direct order
-(the first result is pushed first),
-so that after the call the last result is on the top of the stack.
-<p>
-Any error inside the called function is propagated upwards
-(with a <code>longjmp</code>).
-<p>
-The following example shows how the host program can do the
-equivalent to this Lua code:
-<pre>
-     a = f("how", t.x, 14)
-</pre><p>
-Here it is in&nbsp;C:
-<pre>
-     lua_getfield(L, LUA_GLOBALSINDEX, "f"); /* function to be called */
-     lua_pushstring(L, "how");                        /* 1st argument */
-     lua_getfield(L, LUA_GLOBALSINDEX, "t");   /* table to be indexed */
-     lua_getfield(L, -1, "x");        /* push result of t.x (2nd arg) */
-     lua_remove(L, -2);                  /* remove 't' from the stack */
-     lua_pushinteger(L, 14);                          /* 3rd argument */
-     lua_call(L, 3, 1);     /* call 'f' with 3 arguments and 1 result */
-     lua_setfield(L, LUA_GLOBALSINDEX, "a");        /* set global 'a' */
-</pre><p>
-Note that the code above is "balanced":
-at its end, the stack is back to its original configuration.
-This is considered good programming practice.
-<hr><h3><a name="lua_CFunction"><code>lua_CFunction</code></a></h3>
-<pre>typedef int (*lua_CFunction) (lua_State *L);</pre>
-<p>
-Type for C&nbsp;functions.
-<p>
-In order to communicate properly with Lua,
-a C&nbsp;function must use the following protocol,
-which defines the way parameters and results are passed:
-a C&nbsp;function receives its arguments from Lua in its stack
-in direct order (the first argument is pushed first).
-So, when the function starts,
-<code>lua_gettop(L)</code> returns the number of arguments received by the function.
-The first argument (if any) is at index 1
-and its last argument is at index <code>lua_gettop(L)</code>.
-To return values to Lua, a C&nbsp;function just pushes them onto the stack,
-in direct order (the first result is pushed first),
-and returns the number of results.
-Any other value in the stack below the results will be properly
-discarded by Lua.
-Like a Lua function, a C&nbsp;function called by Lua can also return
-many results.
-<p>
-As an example, the following function receives a variable number
-of numerical arguments and returns their average and sum:
-<pre>
-     static int foo (lua_State *L) {
-       int n = lua_gettop(L);    /* number of arguments */
-       lua_Number sum = 0;
-       int i;
-       for (i = 1; i &lt;= n; i++) {
-         if (!lua_isnumber(L, i)) {
-           lua_pushstring(L, "incorrect argument");
-           lua_error(L);
-         }
-         sum += lua_tonumber(L, i);
-       }
-       lua_pushnumber(L, sum/n);        /* first result */
-       lua_pushnumber(L, sum);         /* second result */
-       return 2;                   /* number of results */
-     }
-</pre>
-<hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p>
-<span class="apii">[-0, +0, <em>m</em>]</span>
-<pre>int lua_checkstack (lua_State *L, int extra);</pre>
-<p>
-Ensures that there are at least <code>extra</code> free stack slots in the stack.
-It returns false if it cannot grow the stack to that size.
-This function never shrinks the stack;
-if the stack is already larger than the new size,
-it is left unchanged.
-<hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>void lua_close (lua_State *L);</pre>
-<p>
-Destroys all objects in the given Lua state
-(calling the corresponding garbage-collection metamethods, if any)
-and frees all dynamic memory used by this state.
-On several platforms, you may not need to call this function,
-because all resources are naturally released when the host program ends.
-On the other hand, long-running programs,
-such as a daemon or a web server,
-might need to release states as soon as they are not needed,
-to avoid growing too large.
-<hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p>
-<span class="apii">[-n, +1, <em>e</em>]</span>
-<pre>void lua_concat (lua_State *L, int n);</pre>
-<p>
-Concatenates the <code>n</code> values at the top of the stack,
-pops them, and leaves the result at the top.
-If <code>n</code>&nbsp;is&nbsp;1, the result is the single value on the stack
-(that is, the function does nothing);
-if <code>n</code> is 0, the result is the empty string.
-Concatenation is performed following the usual semantics of Lua
-(see <a href="#2.5.4">&sect;2.5.4</a>).
-<hr><h3><a name="lua_cpcall"><code>lua_cpcall</code></a></h3><p>
-<span class="apii">[-0, +(0|1), <em>-</em>]</span>
-<pre>int lua_cpcall (lua_State *L, lua_CFunction func, void *ud);</pre>
-<p>
-Calls the C&nbsp;function <code>func</code> in protected mode.
-<code>func</code> starts with only one element in its stack,
-a light userdata containing <code>ud</code>.
-In case of errors,
-<a href="#lua_cpcall"><code>lua_cpcall</code></a> returns the same error codes as <a href="#lua_pcall"><code>lua_pcall</code></a>,
-plus the error object on the top of the stack;
-otherwise, it returns zero, and does not change the stack.
-All values returned by <code>func</code> are discarded.
-<hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre>
-<p>
-Creates a new empty table and pushes it onto the stack.
-The new table has space pre-allocated
-for <code>narr</code> array elements and <code>nrec</code> non-array elements.
-This pre-allocation is useful when you know exactly how many elements
-the table will have.
-Otherwise you can use the function <a href="#lua_newtable"><code>lua_newtable</code></a>.
-<hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p>
-<span class="apii">[-0, +0, <em>m</em>]</span>
-<pre>int lua_dump (lua_State *L, lua_Writer writer, void *data);</pre>
-<p>
-Dumps a function as a binary chunk.
-Receives a Lua function on the top of the stack
-and produces a binary chunk that,
-if loaded again,
-results in a function equivalent to the one dumped.
-As it produces parts of the chunk,
-<a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>)
-with the given <code>data</code>
-to write them.
-<p>
-The value returned is the error code returned by the last
-call to the writer;
-0&nbsp;means no errors.
-<p>
-This function does not pop the Lua function from the stack.
-<hr><h3><a name="lua_equal"><code>lua_equal</code></a></h3><p>
-<span class="apii">[-0, +0, <em>e</em>]</span>
-<pre>int lua_equal (lua_State *L, int index1, int index2);</pre>
-<p>
-Returns 1 if the two values in acceptable indices <code>index1</code> and
-<code>index2</code> are equal,
-following the semantics of the Lua <code>==</code> operator
-(that is, may call metamethods).
-Otherwise returns&nbsp;0.
-Also returns&nbsp;0 if any of the indices is non valid.
-<hr><h3><a name="lua_error"><code>lua_error</code></a></h3><p>
-<span class="apii">[-1, +0, <em>v</em>]</span>
-<pre>int lua_error (lua_State *L);</pre>
-<p>
-Generates a Lua error.
-The error message (which can actually be a Lua value of any type)
-must be on the stack top.
-This function does a long jump,
-and therefore never returns.
-(see <a href="#luaL_error"><code>luaL_error</code></a>).
-<hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p>
-<span class="apii">[-0, +0, <em>e</em>]</span>
-<pre>int lua_gc (lua_State *L, int what, int data);</pre>
-<p>
-Controls the garbage collector.
-<p>
-This function performs several tasks,
-according to the value of the parameter <code>what</code>:
-<ul>
-<li><b><code>LUA_GCSTOP</code>:</b>
-stops the garbage collector.
-</li>
-<li><b><code>LUA_GCRESTART</code>:</b>
-restarts the garbage collector.
-</li>
-<li><b><code>LUA_GCCOLLECT</code>:</b>
-performs a full garbage-collection cycle.
-</li>
-<li><b><code>LUA_GCCOUNT</code>:</b>
-returns the current amount of memory (in Kbytes) in use by Lua.
-</li>
-<li><b><code>LUA_GCCOUNTB</code>:</b>
-returns the remainder of dividing the current amount of bytes of
-memory in use by Lua by 1024.
-</li>
-<li><b><code>LUA_GCSTEP</code>:</b>
-performs an incremental step of garbage collection.
-The step "size" is controlled by <code>data</code>
-(larger values mean more steps) in a non-specified way.
-If you want to control the step size
-you must experimentally tune the value of <code>data</code>.
-The function returns 1 if the step finished a
-garbage-collection cycle.
-</li>
-<li><b><code>LUA_GCSETPAUSE</code>:</b>
-sets <code>data</code> as the new value
-for the <em>pause</em> of the collector (see <a href="#2.10">&sect;2.10</a>).
-The function returns the previous value of the pause.
-</li>
-<li><b><code>LUA_GCSETSTEPMUL</code>:</b>
-sets <code>data</code> as the new value for the <em>step multiplier</em> of
-the collector (see <a href="#2.10">&sect;2.10</a>).
-The function returns the previous value of the step multiplier.
-</li>
-</ul>
-<hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>lua_Alloc lua_getallocf (lua_State *L, void **ud);</pre>
-<p>
-Returns the memory-allocation function of a given state.
-If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the
-opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>.
-<hr><h3><a name="lua_getfenv"><code>lua_getfenv</code></a></h3><p>
-<span class="apii">[-0, +1, <em>-</em>]</span>
-<pre>void lua_getfenv (lua_State *L, int index);</pre>
-<p>
-Pushes onto the stack the environment table of
-the value at the given index.
-<hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p>
-<span class="apii">[-0, +1, <em>e</em>]</span>
-<pre>void lua_getfield (lua_State *L, int index, const char *k);</pre>
-<p>
-Pushes onto the stack the value <code>t[k]</code>,
-where <code>t</code> is the value at the given valid index.
-As in Lua, this function may trigger a metamethod
-for the "index" event (see <a href="#2.8">&sect;2.8</a>).
-<hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p>
-<span class="apii">[-0, +1, <em>e</em>]</span>
-<pre>void lua_getglobal (lua_State *L, const char *name);</pre>
-<p>
-Pushes onto the stack the value of the global <code>name</code>.
-It is defined as a macro:
-<pre>
-     #define lua_getglobal(L,s)  lua_getfield(L, LUA_GLOBALSINDEX, s)
-</pre>
-<hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p>
-<span class="apii">[-0, +(0|1), <em>-</em>]</span>
-<pre>int lua_getmetatable (lua_State *L, int index);</pre>
-<p>
-Pushes onto the stack the metatable of the value at the given
-acceptable index.
-If the index is not valid,
-or if the value does not have a metatable,
-the function returns&nbsp;0 and pushes nothing on the stack.
-<hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p>
-<span class="apii">[-1, +1, <em>e</em>]</span>
-<pre>void lua_gettable (lua_State *L, int index);</pre>
-<p>
-Pushes onto the stack the value <code>t[k]</code>,
-where <code>t</code> is the value at the given valid index
-and <code>k</code> is the value at the top of the stack.
-<p>
-This function pops the key from the stack
-(putting the resulting value in its place).
-As in Lua, this function may trigger a metamethod
-for the "index" event (see <a href="#2.8">&sect;2.8</a>).
-<hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_gettop (lua_State *L);</pre>
-<p>
-Returns the index of the top element in the stack.
-Because indices start at&nbsp;1,
-this result is equal to the number of elements in the stack
-(and so 0&nbsp;means an empty stack).
-<hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p>
-<span class="apii">[-1, +1, <em>-</em>]</span>
-<pre>void lua_insert (lua_State *L, int index);</pre>
-<p>
-Moves the top element into the given valid index,
-shifting up the elements above this index to open space.
-Cannot be called with a pseudo-index,
-because a pseudo-index is not an actual stack position.
-<hr><h3><a name="lua_Integer"><code>lua_Integer</code></a></h3>
-<pre>typedef ptrdiff_t lua_Integer;</pre>
-<p>
-The type used by the Lua API to represent integral values.
-<p>
-By default it is a <code>ptrdiff_t</code>,
-which is usually the largest signed integral type the machine handles
-"comfortably".
-<hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_isboolean (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the value at the given acceptable index has type boolean,
-and 0&nbsp;otherwise.
-<hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_iscfunction (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the value at the given acceptable index is a C&nbsp;function,
-and 0&nbsp;otherwise.
-<hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_isfunction (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the value at the given acceptable index is a function
-(either C or Lua), and 0&nbsp;otherwise.
-<hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_islightuserdata (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the value at the given acceptable index is a light userdata,
-and 0&nbsp;otherwise.
-<hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_isnil (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the value at the given acceptable index is <b>nil</b>,
-and 0&nbsp;otherwise.
-<hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_isnone (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the given acceptable index is not valid
-(that is, it refers to an element outside the current stack),
-and 0&nbsp;otherwise.
-<hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_isnoneornil (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the given acceptable index is not valid
-(that is, it refers to an element outside the current stack)
-or if the value at this index is <b>nil</b>,
-and 0&nbsp;otherwise.
-<hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_isnumber (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the value at the given acceptable index is a number
-or a string convertible to a number,
-and 0&nbsp;otherwise.
-<hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_isstring (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the value at the given acceptable index is a string
-or a number (which is always convertible to a string),
-and 0&nbsp;otherwise.
-<hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_istable (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the value at the given acceptable index is a table,
-and 0&nbsp;otherwise.
-<hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_isthread (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the value at the given acceptable index is a thread,
-and 0&nbsp;otherwise.
-<hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_isuserdata (lua_State *L, int index);</pre>
-<p>
-Returns 1 if the value at the given acceptable index is a userdata
-(either full or light), and 0&nbsp;otherwise.
-<hr><h3><a name="lua_lessthan"><code>lua_lessthan</code></a></h3><p>
-<span class="apii">[-0, +0, <em>e</em>]</span>
-<pre>int lua_lessthan (lua_State *L, int index1, int index2);</pre>
-<p>
-Returns 1 if the value at acceptable index <code>index1</code> is smaller
-than the value at acceptable index <code>index2</code>,
-following the semantics of the Lua <code>&lt;</code> operator
-(that is, may call metamethods).
-Otherwise returns&nbsp;0.
-Also returns&nbsp;0 if any of the indices is non valid.
-<hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p>
-<span class="apii">[-0, +1, <em>-</em>]</span>
-<pre>int lua_load (lua_State *L,
-              lua_Reader reader,
-              void *data,
-              const char *chunkname);</pre>
-<p>
-Loads a Lua chunk.
-If there are no errors,
-<a href="#lua_load"><code>lua_load</code></a> pushes the compiled chunk as a Lua
-function on top of the stack.
-Otherwise, it pushes an error message.
-The return values of <a href="#lua_load"><code>lua_load</code></a> are:
-<ul>
-<li><b>0:</b> no errors;</li>
-<li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>:</b>
-syntax error during pre-compilation;</li>
-<li><b><a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>:</b>
-memory allocation error.</li>
-</ul>
-<p>
-This function only loads a chunk;
-it does not run it.
-<p>
-<a href="#lua_load"><code>lua_load</code></a> automatically detects whether the chunk is text or binary,
-and loads it accordingly (see program <code>luac</code>).
-<p>
-The <a href="#lua_load"><code>lua_load</code></a> function uses a user-supplied <code>reader</code> function
-to read the chunk (see <a href="#lua_Reader"><code>lua_Reader</code></a>).
-The <code>data</code> argument is an opaque value passed to the reader function.
-<p>
-The <code>chunkname</code> argument gives a name to the chunk,
-which is used for error messages and in debug information (see <a href="#3.8">&sect;3.8</a>).
-<hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>lua_State *lua_newstate (lua_Alloc f, void *ud);</pre>
-<p>
-Creates a new, independent state.
-Returns <code>NULL</code> if cannot create the state
-(due to lack of memory).
-The argument <code>f</code> is the allocator function;
-Lua does all memory allocation for this state through this function.
-The second argument, <code>ud</code>, is an opaque pointer that Lua
-simply passes to the allocator in every call.
-<hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>void lua_newtable (lua_State *L);</pre>
-<p>
-Creates a new empty table and pushes it onto the stack.
-It is equivalent to <code>lua_createtable(L, 0, 0)</code>.
-<hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>lua_State *lua_newthread (lua_State *L);</pre>
-<p>
-Creates a new thread, pushes it on the stack,
-and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> that represents this new thread.
-The new state returned by this function shares with the original state
-all global objects (such as tables),
-but has an independent execution stack.
-<p>
-There is no explicit function to close or to destroy a thread.
-Threads are subject to garbage collection,
-like any Lua object.
-<hr><h3><a name="lua_newuserdata"><code>lua_newuserdata</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>void *lua_newuserdata (lua_State *L, size_t size);</pre>
-<p>
-This function allocates a new block of memory with the given size,
-pushes onto the stack a new full userdata with the block address,
-and returns this address.
-<p>
-Userdata represent C&nbsp;values in Lua.
-A <em>full userdata</em> represents a block of memory.
-It is an object (like a table):
-you must create it, it can have its own metatable,
-and you can detect when it is being collected.
-A full userdata is only equal to itself (under raw equality).
-<p>
-When Lua collects a full userdata with a <code>gc</code> metamethod,
-Lua calls the metamethod and marks the userdata as finalized.
-When this userdata is collected again then
-Lua frees its corresponding memory.
-<hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p>
-<span class="apii">[-1, +(2|0), <em>e</em>]</span>
-<pre>int lua_next (lua_State *L, int index);</pre>
-<p>
-Pops a key from the stack,
-and pushes a key-value pair from the table at the given index
-(the "next" pair after the given key).
-If there are no more elements in the table,
-then <a href="#lua_next"><code>lua_next</code></a> returns 0 (and pushes nothing).
-<p>
-A typical traversal looks like this:
-<pre>
-     /* table is in the stack at index 't' */
-     lua_pushnil(L);  /* first key */
-     while (lua_next(L, t) != 0) {
-       /* uses 'key' (at index -2) and 'value' (at index -1) */
-       printf("%s - %s\n",
-              lua_typename(L, lua_type(L, -2)),
-              lua_typename(L, lua_type(L, -1)));
-       /* removes 'value'; keeps 'key' for next iteration */
-       lua_pop(L, 1);
-     }
-</pre>
-<p>
-While traversing a table,
-do not call <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key,
-unless you know that the key is actually a string.
-Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> <em>changes</em>
-the value at the given index;
-this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>.
-<hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3>
-<pre>typedef double lua_Number;</pre>
-<p>
-The type of numbers in Lua.
-By default, it is double, but that can be changed in <code>luaconf.h</code>.
-<p>
-Through the configuration file you can change
-Lua to operate with another type for numbers (e.g., float or long).
-<hr><h3><a name="lua_objlen"><code>lua_objlen</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>size_t lua_objlen (lua_State *L, int index);</pre>
-<p>
-Returns the "length" of the value at the given acceptable index:
-for strings, this is the string length;
-for tables, this is the result of the length operator ('<code>#</code>');
-for userdata, this is the size of the block of memory allocated
-for the userdata;
-for other values, it is&nbsp;0.
-<hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p>
-<span class="apii">[-(nargs + 1), +(nresults|1), <em>-</em>]</span>
-<pre>int lua_pcall (lua_State *L, int nargs, int nresults, int errfunc);</pre>
-<p>
-Calls a function in protected mode.
-<p>
-Both <code>nargs</code> and <code>nresults</code> have the same meaning as
-in <a href="#lua_call"><code>lua_call</code></a>.
-If there are no errors during the call,
-<a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>.
-However, if there is any error,
-<a href="#lua_pcall"><code>lua_pcall</code></a> catches it,
-pushes a single value on the stack (the error message),
-and returns an error code.
-Like <a href="#lua_call"><code>lua_call</code></a>,
-<a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function
-and its arguments from the stack.
-<p>
-If <code>errfunc</code> is 0,
-then the error message returned on the stack
-is exactly the original error message.
-Otherwise, <code>errfunc</code> is the stack index of an
-<em>error handler function</em>.
-(In the current implementation, this index cannot be a pseudo-index.)
-In case of runtime errors,
-this function will be called with the error message
-and its return value will be the message returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>.
-<p>
-Typically, the error handler function is used to add more debug
-information to the error message, such as a stack traceback.
-Such information cannot be gathered after the return of <a href="#lua_pcall"><code>lua_pcall</code></a>,
-since by then the stack has unwound.
-<p>
-The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns 0 in case of success
-or one of the following error codes
-(defined in <code>lua.h</code>):
-<ul>
-<li><b><a name="pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>:</b>
-a runtime error.
-</li>
-<li><b><a name="pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>:</b>
-memory allocation error.
-For such errors, Lua does not call the error handler function.
-</li>
-<li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>:</b>
-error while running the error handler function.
-</li>
-</ul>
-<hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p>
-<span class="apii">[-n, +0, <em>-</em>]</span>
-<pre>void lua_pop (lua_State *L, int n);</pre>
-<p>
-Pops <code>n</code> elements from the stack.
-<hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p>
-<span class="apii">[-0, +1, <em>-</em>]</span>
-<pre>void lua_pushboolean (lua_State *L, int b);</pre>
-<p>
-Pushes a boolean value with value <code>b</code> onto the stack.
-<hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p>
-<span class="apii">[-n, +1, <em>m</em>]</span>
-<pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre>
-<p>
-Pushes a new C&nbsp;closure onto the stack.
-<p>
-When a C&nbsp;function is created,
-it is possible to associate some values with it,
-thus creating a C&nbsp;closure (see <a href="#3.4">&sect;3.4</a>);
-these values are then accessible to the function whenever it is called.
-To associate values with a C&nbsp;function,
-first these values should be pushed onto the stack
-(when there are multiple values, the first value is pushed first).
-Then <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>
-is called to create and push the C&nbsp;function onto the stack,
-with the argument <code>n</code> telling how many values should be
-associated with the function.
-<a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack.
-<p>
-The maximum value for <code>n</code> is 255.
-<hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre>
-<p>
-Pushes a C&nbsp;function onto the stack.
-This function receives a pointer to a C function
-and pushes onto the stack a Lua value of type <code>function</code> that,
-when called, invokes the corresponding C&nbsp;function.
-<p>
-Any function to be registered in Lua must
-follow the correct protocol to receive its parameters
-and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
-<p>
-<code>lua_pushcfunction</code> is defined as a macro:
-<pre>
-     #define lua_pushcfunction(L,f)  lua_pushcclosure(L,f,0)
-</pre>
-<hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>const char *lua_pushfstring (lua_State *L, const char *fmt, ...);</pre>
-<p>
-Pushes onto the stack a formatted string
-and returns a pointer to this string.
-It is similar to the C&nbsp;function <code>sprintf</code>,
-but has some important differences:
-<ul>
-<li>
-You do not have to allocate space for the result:
-the result is a Lua string and Lua takes care of memory allocation
-(and deallocation, through garbage collection).
-</li>
-<li>
-The conversion specifiers are quite restricted.
-There are no flags, widths, or precisions.
-The conversion specifiers can only be
-'<code>%%</code>' (inserts a '<code>%</code>' in the string),
-'<code>%s</code>' (inserts a zero-terminated string, with no size restrictions),
-'<code>%f</code>' (inserts a <a href="#lua_Number"><code>lua_Number</code></a>),
-'<code>%p</code>' (inserts a pointer as a hexadecimal numeral),
-'<code>%d</code>' (inserts an <code>int</code>), and
-'<code>%c</code>' (inserts an <code>int</code> as a character).
-</li>
-</ul>
-<hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p>
-<span class="apii">[-0, +1, <em>-</em>]</span>
-<pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre>
-<p>
-Pushes a number with value <code>n</code> onto the stack.
-<hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p>
-<span class="apii">[-0, +1, <em>-</em>]</span>
-<pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre>
-<p>
-Pushes a light userdata onto the stack.
-<p>
-Userdata represent C&nbsp;values in Lua.
-A <em>light userdata</em> represents a pointer.
-It is a value (like a number):
-you do not create it, it has no individual metatable,
-and it is not collected (as it was never created).
-A light userdata is equal to "any"
-light userdata with the same C&nbsp;address.
-<hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>void lua_pushliteral (lua_State *L, const char *s);</pre>
-<p>
-This macro is equivalent to <a href="#lua_pushlstring"><code>lua_pushlstring</code></a>,
-but can be used only when <code>s</code> is a literal string.
-In these cases, it automatically provides the string length.
-<hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>void lua_pushlstring (lua_State *L, const char *s, size_t len);</pre>
-<p>
-Pushes the string pointed to by <code>s</code> with size <code>len</code>
-onto the stack.
-Lua makes (or reuses) an internal copy of the given string,
-so the memory at <code>s</code> can be freed or reused immediately after
-the function returns.
-The string can contain embedded zeros.
-<hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p>
-<span class="apii">[-0, +1, <em>-</em>]</span>
-<pre>void lua_pushnil (lua_State *L);</pre>
-<p>
-Pushes a nil value onto the stack.
-<hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p>
-<span class="apii">[-0, +1, <em>-</em>]</span>
-<pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre>
-<p>
-Pushes a number with value <code>n</code> onto the stack.
-<hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>void lua_pushstring (lua_State *L, const char *s);</pre>
-<p>
-Pushes the zero-terminated string pointed to by <code>s</code>
-onto the stack.
-Lua makes (or reuses) an internal copy of the given string,
-so the memory at <code>s</code> can be freed or reused immediately after
-the function returns.
-The string cannot contain embedded zeros;
-it is assumed to end at the first zero.
-<hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p>
-<span class="apii">[-0, +1, <em>-</em>]</span>
-<pre>int lua_pushthread (lua_State *L);</pre>
-<p>
-Pushes the thread represented by <code>L</code> onto the stack.
-Returns 1 if this thread is the main thread of its state.
-<hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p>
-<span class="apii">[-0, +1, <em>-</em>]</span>
-<pre>void lua_pushvalue (lua_State *L, int index);</pre>
-<p>
-Pushes a copy of the element at the given valid index
-onto the stack.
-<hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>const char *lua_pushvfstring (lua_State *L,
-                              const char *fmt,
-                              va_list argp);</pre>
-<p>
-Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code>
-instead of a variable number of arguments.
-<hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre>
-<p>
-Returns 1 if the two values in acceptable indices <code>index1</code> and
-<code>index2</code> are primitively equal
-(that is, without calling metamethods).
-Otherwise returns&nbsp;0.
-Also returns&nbsp;0 if any of the indices are non valid.
-<hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p>
-<span class="apii">[-1, +1, <em>-</em>]</span>
-<pre>void lua_rawget (lua_State *L, int index);</pre>
-<p>
-Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access
-(i.e., without metamethods).
-<hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p>
-<span class="apii">[-0, +1, <em>-</em>]</span>
-<pre>void lua_rawgeti (lua_State *L, int index, int n);</pre>
-<p>
-Pushes onto the stack the value <code>t[n]</code>,
-where <code>t</code> is the value at the given valid index.
-The access is raw;
-that is, it does not invoke metamethods.
-<hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p>
-<span class="apii">[-2, +0, <em>m</em>]</span>
-<pre>void lua_rawset (lua_State *L, int index);</pre>
-<p>
-Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment
-(i.e., without metamethods).
-<hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p>
-<span class="apii">[-1, +0, <em>m</em>]</span>
-<pre>void lua_rawseti (lua_State *L, int index, int n);</pre>
-<p>
-Does the equivalent of <code>t[n] = v</code>,
-where <code>t</code> is the value at the given valid index
-and <code>v</code> is the value at the top of the stack.
-<p>
-This function pops the value from the stack.
-The assignment is raw;
-that is, it does not invoke metamethods.
-<hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3>
-<pre>typedef const char * (*lua_Reader) (lua_State *L,
-                                    void *data,
-                                    size_t *size);</pre>
-<p>
-The reader function used by <a href="#lua_load"><code>lua_load</code></a>.
-Every time it needs another piece of the chunk,
-<a href="#lua_load"><code>lua_load</code></a> calls the reader,
-passing along its <code>data</code> parameter.
-The reader must return a pointer to a block of memory
-with a new piece of the chunk
-and set <code>size</code> to the block size.
-The block must exist until the reader function is called again.
-To signal the end of the chunk,
-the reader must return <code>NULL</code> or set <code>size</code> to zero.
-The reader function may return pieces of any size greater than zero.
-<hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p>
-<span class="apii">[-0, +0, <em>e</em>]</span>
-<pre>void lua_register (lua_State *L,
-                   const char *name,
-                   lua_CFunction f);</pre>
-<p>
-Sets the C function <code>f</code> as the new value of global <code>name</code>.
-It is defined as a macro:
-<pre>
-     #define lua_register(L,n,f) \
-            (lua_pushcfunction(L, f), lua_setglobal(L, n))
-</pre>
-<hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p>
-<span class="apii">[-1, +0, <em>-</em>]</span>
-<pre>void lua_remove (lua_State *L, int index);</pre>
-<p>
-Removes the element at the given valid index,
-shifting down the elements above this index to fill the gap.
-Cannot be called with a pseudo-index,
-because a pseudo-index is not an actual stack position.
-<hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p>
-<span class="apii">[-1, +0, <em>-</em>]</span>
-<pre>void lua_replace (lua_State *L, int index);</pre>
-<p>
-Moves the top element into the given position (and pops it),
-without shifting any element
-(therefore replacing the value at the given position).
-<hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p>
-<span class="apii">[-?, +?, <em>-</em>]</span>
-<pre>int lua_resume (lua_State *L, int narg);</pre>
-<p>
-Starts and resumes a coroutine in a given thread.
-<p>
-To start a coroutine, you first create a new thread
-(see <a href="#lua_newthread"><code>lua_newthread</code></a>);
-then you push onto its stack the main function plus any arguments;
-then you call <a href="#lua_resume"><code>lua_resume</code></a>,
-with <code>narg</code> being the number of arguments.
-This call returns when the coroutine suspends or finishes its execution.
-When it returns, the stack contains all values passed to <a href="#lua_yield"><code>lua_yield</code></a>,
-or all values returned by the body function.
-<a href="#lua_resume"><code>lua_resume</code></a> returns
-<a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the coroutine yields,
-0 if the coroutine finishes its execution
-without errors,
-or an error code in case of errors (see <a href="#lua_pcall"><code>lua_pcall</code></a>).
-In case of errors,
-the stack is not unwound,
-so you can use the debug API over it.
-The error message is on the top of the stack.
-To restart a coroutine, you put on its stack only the values to
-be passed as results from <code>yield</code>,
-and then call <a href="#lua_resume"><code>lua_resume</code></a>.
-<hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);</pre>
-<p>
-Changes the allocator function of a given state to <code>f</code>
-with user data <code>ud</code>.
-<hr><h3><a name="lua_setfenv"><code>lua_setfenv</code></a></h3><p>
-<span class="apii">[-1, +0, <em>-</em>]</span>
-<pre>int lua_setfenv (lua_State *L, int index);</pre>
-<p>
-Pops a table from the stack and sets it as
-the new environment for the value at the given index.
-If the value at the given index is
-neither a function nor a thread nor a userdata,
-<a href="#lua_setfenv"><code>lua_setfenv</code></a> returns 0.
-Otherwise it returns 1.
-<hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p>
-<span class="apii">[-1, +0, <em>e</em>]</span>
-<pre>void lua_setfield (lua_State *L, int index, const char *k);</pre>
-<p>
-Does the equivalent to <code>t[k] = v</code>,
-where <code>t</code> is the value at the given valid index
-and <code>v</code> is the value at the top of the stack.
-<p>
-This function pops the value from the stack.
-As in Lua, this function may trigger a metamethod
-for the "newindex" event (see <a href="#2.8">&sect;2.8</a>).
-<hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p>
-<span class="apii">[-1, +0, <em>e</em>]</span>
-<pre>void lua_setglobal (lua_State *L, const char *name);</pre>
-<p>
-Pops a value from the stack and
-sets it as the new value of global <code>name</code>.
-It is defined as a macro:
-<pre>
-     #define lua_setglobal(L,s)   lua_setfield(L, LUA_GLOBALSINDEX, s)
-</pre>
-<hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p>
-<span class="apii">[-1, +0, <em>-</em>]</span>
-<pre>int lua_setmetatable (lua_State *L, int index);</pre>
-<p>
-Pops a table from the stack and
-sets it as the new metatable for the value at the given
-acceptable index.
-<hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p>
-<span class="apii">[-2, +0, <em>e</em>]</span>
-<pre>void lua_settable (lua_State *L, int index);</pre>
-<p>
-Does the equivalent to <code>t[k] = v</code>,
-where <code>t</code> is the value at the given valid index,
-<code>v</code> is the value at the top of the stack,
-and <code>k</code> is the value just below the top.
-<p>
-This function pops both the key and the value from the stack.
-As in Lua, this function may trigger a metamethod
-for the "newindex" event (see <a href="#2.8">&sect;2.8</a>).
-<hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p>
-<span class="apii">[-?, +?, <em>-</em>]</span>
-<pre>void lua_settop (lua_State *L, int index);</pre>
-<p>
-Accepts any acceptable index, or&nbsp;0,
-and sets the stack top to this index.
-If the new top is larger than the old one,
-then the new elements are filled with <b>nil</b>.
-If <code>index</code> is&nbsp;0, then all stack elements are removed.
-<hr><h3><a name="lua_State"><code>lua_State</code></a></h3>
-<pre>typedef struct lua_State lua_State;</pre>
-<p>
-Opaque structure that keeps the whole state of a Lua interpreter.
-The Lua library is fully reentrant:
-it has no global variables.
-All information about a state is kept in this structure.
-<p>
-A pointer to this state must be passed as the first argument to
-every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>,
-which creates a Lua state from scratch.
-<hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_status (lua_State *L);</pre>
-<p>
-Returns the status of the thread <code>L</code>.
-<p>
-The status can be 0 for a normal thread,
-an error code if the thread finished its execution with an error,
-or <a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended.
-<hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_toboolean (lua_State *L, int index);</pre>
-<p>
-Converts the Lua value at the given acceptable index to a C&nbsp;boolean
-value (0&nbsp;or&nbsp;1).
-Like all tests in Lua,
-<a href="#lua_toboolean"><code>lua_toboolean</code></a> returns 1 for any Lua value
-different from <b>false</b> and <b>nil</b>;
-otherwise it returns 0.
-It also returns 0 when called with a non-valid index.
-(If you want to accept only actual boolean values,
-use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.)
-<hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre>
-<p>
-Converts a value at the given acceptable index to a C&nbsp;function.
-That value must be a C&nbsp;function;
-otherwise, returns <code>NULL</code>.
-<hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre>
-<p>
-Converts the Lua value at the given acceptable index
-to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>.
-The Lua value must be a number or a string convertible to a number
-(see <a href="#2.2.1">&sect;2.2.1</a>);
-otherwise, <a href="#lua_tointeger"><code>lua_tointeger</code></a> returns&nbsp;0.
-<p>
-If the number is not an integer,
-it is truncated in some non-specified way.
-<hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p>
-<span class="apii">[-0, +0, <em>m</em>]</span>
-<pre>const char *lua_tolstring (lua_State *L, int index, size_t *len);</pre>
-<p>
-Converts the Lua value at the given acceptable index to a C&nbsp;string.
-If <code>len</code> is not <code>NULL</code>,
-it also sets <code>*len</code> with the string length.
-The Lua value must be a string or a number;
-otherwise, the function returns <code>NULL</code>.
-If the value is a number,
-then <a href="#lua_tolstring"><code>lua_tolstring</code></a> also
-<em>changes the actual value in the stack to a string</em>.
-(This change confuses <a href="#lua_next"><code>lua_next</code></a>
-when <a href="#lua_tolstring"><code>lua_tolstring</code></a> is applied to keys during a table traversal.)
-<p>
-<a href="#lua_tolstring"><code>lua_tolstring</code></a> returns a fully aligned pointer
-to a string inside the Lua state.
-This string always has a zero ('<code>\0</code>')
-after its last character (as in&nbsp;C),
-but can contain other zeros in its body.
-Because Lua has garbage collection,
-there is no guarantee that the pointer returned by <a href="#lua_tolstring"><code>lua_tolstring</code></a>
-will be valid after the corresponding value is removed from the stack.
-<hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>lua_Number lua_tonumber (lua_State *L, int index);</pre>
-<p>
-Converts the Lua value at the given acceptable index
-to the C&nbsp;type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>).
-The Lua value must be a number or a string convertible to a number
-(see <a href="#2.2.1">&sect;2.2.1</a>);
-otherwise, <a href="#lua_tonumber"><code>lua_tonumber</code></a> returns&nbsp;0.
-<hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>const void *lua_topointer (lua_State *L, int index);</pre>
-<p>
-Converts the value at the given acceptable index to a generic
-C&nbsp;pointer (<code>void*</code>).
-The value can be a userdata, a table, a thread, or a function;
-otherwise, <a href="#lua_topointer"><code>lua_topointer</code></a> returns <code>NULL</code>.
-Different objects will give different pointers.
-There is no way to convert the pointer back to its original value.
-<p>
-Typically this function is used only for debug information.
-<hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p>
-<span class="apii">[-0, +0, <em>m</em>]</span>
-<pre>const char *lua_tostring (lua_State *L, int index);</pre>
-<p>
-Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>.
-<hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>lua_State *lua_tothread (lua_State *L, int index);</pre>
-<p>
-Converts the value at the given acceptable index to a Lua thread
-(represented as <code>lua_State*</code>).
-This value must be a thread;
-otherwise, the function returns <code>NULL</code>.
-<hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>void *lua_touserdata (lua_State *L, int index);</pre>
-<p>
-If the value at the given acceptable index is a full userdata,
-returns its block address.
-If the value is a light userdata,
-returns its pointer.
-Otherwise, returns <code>NULL</code>.
-<hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_type (lua_State *L, int index);</pre>
-<p>
-Returns the type of the value in the given acceptable index,
-or <code>LUA_TNONE</code> for a non-valid index
-(that is, an index to an "empty" stack position).
-The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants
-defined in <code>lua.h</code>:
-<code>LUA_TNIL</code>,
-<code>LUA_TNUMBER</code>,
-<code>LUA_TBOOLEAN</code>,
-<code>LUA_TSTRING</code>,
-<code>LUA_TTABLE</code>,
-<code>LUA_TFUNCTION</code>,
-<code>LUA_TUSERDATA</code>,
-<code>LUA_TTHREAD</code>,
-and
-<code>LUA_TLIGHTUSERDATA</code>.
-<hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>const char *lua_typename  (lua_State *L, int tp);</pre>
-<p>
-Returns the name of the type encoded by the value <code>tp</code>,
-which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>.
-<hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3>
-<pre>typedef int (*lua_Writer) (lua_State *L,
-                           const void* p,
-                           size_t sz,
-                           void* ud);</pre>
-<p>
-The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>.
-Every time it produces another piece of chunk,
-<a href="#lua_dump"><code>lua_dump</code></a> calls the writer,
-passing along the buffer to be written (<code>p</code>),
-its size (<code>sz</code>),
-and the <code>data</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>.
-<p>
-The writer returns an error code:
-0&nbsp;means no errors;
-any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from
-calling the writer again.
-<hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p>
-<span class="apii">[-?, +?, <em>-</em>]</span>
-<pre>void lua_xmove (lua_State *from, lua_State *to, int n);</pre>
-<p>
-Exchange values between different threads of the <em>same</em> global state.
-<p>
-This function pops <code>n</code> values from the stack <code>from</code>,
-and pushes them onto the stack <code>to</code>.
-<hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p>
-<span class="apii">[-?, +?, <em>-</em>]</span>
-<pre>int lua_yield  (lua_State *L, int nresults);</pre>
-<p>
-Yields a coroutine.
-<p>
-This function should only be called as the
-return expression of a C&nbsp;function, as follows:
-<pre>
-     return lua_yield (L, nresults);
-</pre><p>
-When a C&nbsp;function calls <a href="#lua_yield"><code>lua_yield</code></a> in that way,
-the running coroutine suspends its execution,
-and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns.
-The parameter <code>nresults</code> is the number of values from the stack
-that are passed as results to <a href="#lua_resume"><code>lua_resume</code></a>.
-<h2>3.8 - <a name="3.8">The Debug Interface</a></h2>
-<p>
-Lua has no built-in debugging facilities.
-Instead, it offers a special interface
-by means of functions and <em>hooks</em>.
-This interface allows the construction of different
-kinds of debuggers, profilers, and other tools
-that need "inside information" from the interpreter.
-<hr><h3><a name="lua_Debug"><code>lua_Debug</code></a></h3>
-<pre>typedef struct lua_Debug {
-  int event;
-  const char *name;           /* (n) */
-  const char *namewhat;       /* (n) */
-  const char *what;           /* (S) */
-  const char *source;         /* (S) */
-  int currentline;            /* (l) */
-  int nups;                   /* (u) number of upvalues */
-  int linedefined;            /* (S) */
-  int lastlinedefined;        /* (S) */
-  char short_src[LUA_IDSIZE]; /* (S) */
-  /* private part */
-  <em>other fields</em>
-} lua_Debug;</pre>
-<p>
-A structure used to carry different pieces of
-information about an active function.
-<a href="#lua_getstack"><code>lua_getstack</code></a> fills only the private part
-of this structure, for later use.
-To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information,
-call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
-<p>
-The fields of <a href="#lua_Debug"><code>lua_Debug</code></a> have the following meaning:
-<ul>
-<li><b><code>source</code>:</b>
-If the function was defined in a string,
-then <code>source</code> is that string.
-If the function was defined in a file,
-then <code>source</code> starts with a '<code>@</code>' followed by the file name.
-</li>
-<li><b><code>short_src</code>:</b>
-a "printable" version of <code>source</code>, to be used in error messages.
-</li>
-<li><b><code>linedefined</code>:</b>
-the line number where the definition of the function starts.
-</li>
-<li><b><code>lastlinedefined</code>:</b>
-the line number where the definition of the function ends.
-</li>
-<li><b><code>what</code>:</b>
-the string <code>"Lua"</code> if the function is a Lua function,
-<code>"C"</code> if it is a C&nbsp;function,
-<code>"main"</code> if it is the main part of a chunk,
-and <code>"tail"</code> if it was a function that did a tail call.
-In the latter case,
-Lua has no other information about the function.
-</li>
-<li><b><code>currentline</code>:</b>
-the current line where the given function is executing.
-When no line information is available,
-<code>currentline</code> is set to -1.
-</li>
-<li><b><code>name</code>:</b>
-a reasonable name for the given function.
-Because functions in Lua are first-class values,
-they do not have a fixed name:
-some functions can be the value of multiple global variables,
-while others can be stored only in a table field.
-The <code>lua_getinfo</code> function checks how the function was
-called to find a suitable name.
-If it cannot find a name,
-then <code>name</code> is set to <code>NULL</code>.
-</li>
-<li><b><code>namewhat</code>:</b>
-explains the <code>name</code> field.
-The value of <code>namewhat</code> can be
-<code>"global"</code>, <code>"local"</code>, <code>"method"</code>,
-<code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string),
-according to how the function was called.
-(Lua uses the empty string when no other option seems to apply.)
-</li>
-<li><b><code>nups</code>:</b>
-the number of upvalues of the function.
-</li>
-</ul>
-<hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>lua_Hook lua_gethook (lua_State *L);</pre>
-<p>
-Returns the current hook function.
-<hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_gethookcount (lua_State *L);</pre>
-<p>
-Returns the current hook count.
-<hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_gethookmask (lua_State *L);</pre>
-<p>
-Returns the current hook mask.
-<hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p>
-<span class="apii">[-(0|1), +(0|1|2), <em>m</em>]</span>
-<pre>int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);</pre>
-<p>
-Returns information about a specific function or function invocation.
-<p>
-To get information about a function invocation,
-the parameter <code>ar</code> must be a valid activation record that was
-filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
-given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
-<p>
-To get information about a function you push it onto the stack
-and start the <code>what</code> string with the character '<code>&gt;</code>'.
-(In that case,
-<code>lua_getinfo</code> pops the function in the top of the stack.)
-For instance, to know in which line a function <code>f</code> was defined,
-you can write the following code:
-<pre>
-     lua_Debug ar;
-     lua_getfield(L, LUA_GLOBALSINDEX, "f");  /* get global 'f' */
-     lua_getinfo(L, "&gt;S", &amp;ar);
-     printf("%d\n", ar.linedefined);
-</pre>
-<p>
-Each character in the string <code>what</code>
-selects some fields of the structure <code>ar</code> to be filled or
-a value to be pushed on the stack:
-<ul>
-<li><b>'<code>n</code>':</b> fills in the field <code>name</code> and <code>namewhat</code>;
-</li>
-<li><b>'<code>S</code>':</b>
-fills in the fields <code>source</code>, <code>short_src</code>,
-<code>linedefined</code>, <code>lastlinedefined</code>, and <code>what</code>;
-</li>
-<li><b>'<code>l</code>':</b> fills in the field <code>currentline</code>;
-</li>
-<li><b>'<code>u</code>':</b> fills in the field <code>nups</code>;
-</li>
-<li><b>'<code>f</code>':</b>
-pushes onto the stack the function that is
-running at the given level;
-</li>
-<li><b>'<code>L</code>':</b>
-pushes onto the stack a table whose indices are the
-numbers of the lines that are valid on the function.
-(A <em>valid line</em> is a line with some associated code,
-that is, a line where you can put a break point.
-Non-valid lines include empty lines and comments.)
-</li>
-</ul>
-<p>
-This function returns 0 on error
-(for instance, an invalid option in <code>what</code>).
-<hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p>
-<span class="apii">[-0, +(0|1), <em>-</em>]</span>
-<pre>const char *lua_getlocal (lua_State *L, lua_Debug *ar, int n);</pre>
-<p>
-Gets information about a local variable of a given activation record.
-The parameter <code>ar</code> must be a valid activation record that was
-filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
-given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
-The index <code>n</code> selects which local variable to inspect
-(1 is the first parameter or active local variable, and so on,
-until the last active local variable).
-<a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack
-and returns its name.
-<p>
-Variable names starting with '<code>(</code>' (open parentheses)
-represent internal variables
-(loop control variables, temporaries, and C&nbsp;function locals).
-<p>
-Returns <code>NULL</code> (and pushes nothing)
-when the index is greater than
-the number of active local variables.
-<hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_getstack (lua_State *L, int level, lua_Debug *ar);</pre>
-<p>
-Get information about the interpreter runtime stack.
-<p>
-This function fills parts of a <a href="#lua_Debug"><code>lua_Debug</code></a> structure with
-an identification of the <em>activation record</em>
-of the function executing at a given level.
-Level&nbsp;0 is the current running function,
-whereas level <em>n+1</em> is the function that has called level <em>n</em>.
-When there are no errors, <a href="#lua_getstack"><code>lua_getstack</code></a> returns 1;
-when called with a level greater than the stack depth,
-it returns 0.
-<hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p>
-<span class="apii">[-0, +(0|1), <em>-</em>]</span>
-<pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre>
-<p>
-Gets information about a closure's upvalue.
-(For Lua functions,
-upvalues are the external local variables that the function uses,
-and that are consequently included in its closure.)
-<a href="#lua_getupvalue"><code>lua_getupvalue</code></a> gets the index <code>n</code> of an upvalue,
-pushes the upvalue's value onto the stack,
-and returns its name.
-<code>funcindex</code> points to the closure in the stack.
-(Upvalues have no particular order,
-as they are active through the whole function.
-So, they are numbered in an arbitrary order.)
-<p>
-Returns <code>NULL</code> (and pushes nothing)
-when the index is greater than the number of upvalues.
-For C&nbsp;functions, this function uses the empty string <code>""</code>
-as a name for all upvalues.
-<hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3>
-<pre>typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);</pre>
-<p>
-Type for debugging hook functions.
-<p>
-Whenever a hook is called, its <code>ar</code> argument has its field
-<code>event</code> set to the specific event that triggered the hook.
-Lua identifies these events with the following constants:
-<a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>,
-<a name="pdf-LUA_HOOKTAILRET"><code>LUA_HOOKTAILRET</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>,
-and <a name="pdf-LUA_HOOKCOUNT"><code>LUA_HOOKCOUNT</code></a>.
-Moreover, for line events, the field <code>currentline</code> is also set.
-To get the value of any other field in <code>ar</code>,
-the hook must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
-For return events, <code>event</code> can be <code>LUA_HOOKRET</code>,
-the normal value, or <code>LUA_HOOKTAILRET</code>.
-In the latter case, Lua is simulating a return from
-a function that did a tail call;
-in this case, it is useless to call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
-<p>
-While Lua is running a hook, it disables other calls to hooks.
-Therefore, if a hook calls back Lua to execute a function or a chunk,
-this execution occurs without any calls to hooks.
-<hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>int lua_sethook (lua_State *L, lua_Hook f, int mask, int count);</pre>
-<p>
-Sets the debugging hook function.
-<p>
-Argument <code>f</code> is the hook function.
-<code>mask</code> specifies on which events the hook will be called:
-it is formed by a bitwise or of the constants
-<a name="pdf-LUA_MASKCALL"><code>LUA_MASKCALL</code></a>,
-<a name="pdf-LUA_MASKRET"><code>LUA_MASKRET</code></a>,
-<a name="pdf-LUA_MASKLINE"><code>LUA_MASKLINE</code></a>,
-and <a name="pdf-LUA_MASKCOUNT"><code>LUA_MASKCOUNT</code></a>.
-The <code>count</code> argument is only meaningful when the mask
-includes <code>LUA_MASKCOUNT</code>.
-For each event, the hook is called as explained below:
-<ul>
-<li><b>The call hook:</b> is called when the interpreter calls a function.
-The hook is called just after Lua enters the new function,
-before the function gets its arguments.
-</li>
-<li><b>The return hook:</b> is called when the interpreter returns from a function.
-The hook is called just before Lua leaves the function.
-You have no access to the values to be returned by the function.
-</li>
-<li><b>The line hook:</b> is called when the interpreter is about to
-start the execution of a new line of code,
-or when it jumps back in the code (even to the same line).
-(This event only happens while Lua is executing a Lua function.)
-</li>
-<li><b>The count hook:</b> is called after the interpreter executes every
-<code>count</code> instructions.
-(This event only happens while Lua is executing a Lua function.)
-</li>
-</ul>
-<p>
-A hook is disabled by setting <code>mask</code> to zero.
-<hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p>
-<span class="apii">[-(0|1), +0, <em>-</em>]</span>
-<pre>const char *lua_setlocal (lua_State *L, lua_Debug *ar, int n);</pre>
-<p>
-Sets the value of a local variable of a given activation record.
-Parameters <code>ar</code> and <code>n</code> are as in <a href="#lua_getlocal"><code>lua_getlocal</code></a>
-(see <a href="#lua_getlocal"><code>lua_getlocal</code></a>).
-<a href="#lua_setlocal"><code>lua_setlocal</code></a> assigns the value at the top of the stack
-to the variable and returns its name.
-It also pops the value from the stack.
-<p>
-Returns <code>NULL</code> (and pops nothing)
-when the index is greater than
-the number of active local variables.
-<hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p>
-<span class="apii">[-(0|1), +0, <em>-</em>]</span>
-<pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre>
-<p>
-Sets the value of a closure's upvalue.
-It assigns the value at the top of the stack
-to the upvalue and returns its name.
-It also pops the value from the stack.
-Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
-(see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>).
-<p>
-Returns <code>NULL</code> (and pops nothing)
-when the index is greater than the number of upvalues.
-<h1>4 - <a name="4">The Auxiliary Library</a></h1>
-<p>
-The <em>auxiliary library</em> provides several convenient functions
-to interface C with Lua.
-While the basic API provides the primitive functions for all 
-interactions between C and Lua,
-the auxiliary library provides higher-level functions for some
-common tasks.
-<p>
-All functions from the auxiliary library
-are defined in header file <code>lauxlib.h</code> and
-have a prefix <code>luaL_</code>.
-<p>
-All functions in the auxiliary library are built on
-top of the basic API,
-and so they provide nothing that cannot be done with this API.
-<p>
-Several functions in the auxiliary library are used to
-check C&nbsp;function arguments.
-Their names are always <code>luaL_check*</code> or <code>luaL_opt*</code>.
-All of these functions throw an error if the check is not satisfied.
-Because the error message is formatted for arguments
-(e.g., "<code>bad argument #1</code>"),
-you should not use these functions for other stack values.
-<h2>4.1 - <a name="4.1">Functions and Types</a></h2>
-<p>
-Here we list all functions and types from the auxiliary library
-in alphabetical order.
-<hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p>
-<span class="apii">[-0, +0, <em>m</em>]</span>
-<pre>void luaL_addchar (luaL_Buffer *B, char c);</pre>
-<p>
-Adds the character <code>c</code> to the buffer <code>B</code>
-(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
-<hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p>
-<span class="apii">[-0, +0, <em>m</em>]</span>
-<pre>void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);</pre>
-<p>
-Adds the string pointed to by <code>s</code> with length <code>l</code> to
-the buffer <code>B</code>
-(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
-The string may contain embedded zeros.
-<hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p>
-<span class="apii">[-0, +0, <em>m</em>]</span>
-<pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre>
-<p>
-Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>)
-a string of length <code>n</code> previously copied to the
-buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>).
-<hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p>
-<span class="apii">[-0, +0, <em>m</em>]</span>
-<pre>void luaL_addstring (luaL_Buffer *B, const char *s);</pre>
-<p>
-Adds the zero-terminated string pointed to by <code>s</code>
-to the buffer <code>B</code>
-(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
-The string may not contain embedded zeros.
-<hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p>
-<span class="apii">[-1, +0, <em>m</em>]</span>
-<pre>void luaL_addvalue (luaL_Buffer *B);</pre>
-<p>
-Adds the value at the top of the stack
-to the buffer <code>B</code>
-(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
-Pops the value.
-<p>
-This is the only function on string buffers that can (and must)
-be called with an extra element on the stack,
-which is the value to be added to the buffer.
-<hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>void luaL_argcheck (lua_State *L,
-                    int cond,
-                    int narg,
-                    const char *extramsg);</pre>
-<p>
-Checks whether <code>cond</code> is true.
-If not, raises an error with the following message,
-where <code>func</code> is retrieved from the call stack:
-<pre>
-     bad argument #&lt;narg&gt; to &lt;func&gt; (&lt;extramsg&gt;)
-</pre>
-<hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>int luaL_argerror (lua_State *L, int narg, const char *extramsg);</pre>
-<p>
-Raises an error with the following message,
-where <code>func</code> is retrieved from the call stack:
-<pre>
-     bad argument #&lt;narg&gt; to &lt;func&gt; (&lt;extramsg&gt;)
-</pre>
-<p>
-This function never returns,
-but it is an idiom to use it in C&nbsp;functions
-as <code>return luaL_argerror(<em>args</em>)</code>.
-<hr><h3><a name="luaL_Buffer"><code>luaL_Buffer</code></a></h3>
-<pre>typedef struct luaL_Buffer luaL_Buffer;</pre>
-<p>
-Type for a <em>string buffer</em>.
-<p>
-A string buffer allows C&nbsp;code to build Lua strings piecemeal.
-Its pattern of use is as follows:
-<ul>
-<li>First you declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
-<li>Then you initialize it with a call <code>luaL_buffinit(L, &amp;b)</code>.</li>
-<li>
-Then you add string pieces to the buffer calling any of
-the <code>luaL_add*</code> functions.
-</li>
-<li>
-You finish by calling <code>luaL_pushresult(&amp;b)</code>.
-This call leaves the final string on the top of the stack.
-</li>
-</ul>
-<p>
-During its normal operation,
-a string buffer uses a variable number of stack slots.
-So, while using a buffer, you cannot assume that you know where
-the top of the stack is.
-You can use the stack between successive calls to buffer operations
-as long as that use is balanced;
-that is,
-when you call a buffer operation,
-the stack is at the same level
-it was immediately after the previous buffer operation.
-(The only exception to this rule is <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.)
-After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its
-level when the buffer was initialized,
-plus the final string on its top.
-<hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>void luaL_buffinit (lua_State *L, luaL_Buffer *B);</pre>
-<p>
-Initializes a buffer <code>B</code>.
-This function does not allocate any space;
-the buffer must be declared as a variable
-(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
-<hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p>
-<span class="apii">[-0, +(0|1), <em>e</em>]</span>
-<pre>int luaL_callmeta (lua_State *L, int obj, const char *e);</pre>
-<p>
-Calls a metamethod.
-<p>
-If the object at index <code>obj</code> has a metatable and this
-metatable has a field <code>e</code>,
-this function calls this field and passes the object as its only argument.
-In this case this function returns 1 and pushes onto the
-stack the value returned by the call.
-If there is no metatable or no metamethod,
-this function returns 0 (without pushing any value on the stack).
-<hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>void luaL_checkany (lua_State *L, int narg);</pre>
-<p>
-Checks whether the function has an argument
-of any type (including <b>nil</b>) at position <code>narg</code>.
-<hr><h3><a name="luaL_checkint"><code>luaL_checkint</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>int luaL_checkint (lua_State *L, int narg);</pre>
-<p>
-Checks whether the function argument <code>narg</code> is a number
-and returns this number cast to an <code>int</code>.
-<hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>lua_Integer luaL_checkinteger (lua_State *L, int narg);</pre>
-<p>
-Checks whether the function argument <code>narg</code> is a number
-and returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>.
-<hr><h3><a name="luaL_checklong"><code>luaL_checklong</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>long luaL_checklong (lua_State *L, int narg);</pre>
-<p>
-Checks whether the function argument <code>narg</code> is a number
-and returns this number cast to a <code>long</code>.
-<hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>const char *luaL_checklstring (lua_State *L, int narg, size_t *l);</pre>
-<p>
-Checks whether the function argument <code>narg</code> is a string
-and returns this string;
-if <code>l</code> is not <code>NULL</code> fills <code>*l</code>
-with the string's length.
-<p>
-This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
-so all conversions and caveats of that function apply here.
-<hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>lua_Number luaL_checknumber (lua_State *L, int narg);</pre>
-<p>
-Checks whether the function argument <code>narg</code> is a number
-and returns this number.
-<hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>int luaL_checkoption (lua_State *L,
-                      int narg,
-                      const char *def,
-                      const char *const lst[]);</pre>
-<p>
-Checks whether the function argument <code>narg</code> is a string and
-searches for this string in the array <code>lst</code>
-(which must be NULL-terminated).
-Returns the index in the array where the string was found.
-Raises an error if the argument is not a string or
-if the string cannot be found.
-<p>
-If <code>def</code> is not <code>NULL</code>,
-the function uses <code>def</code> as a default value when
-there is no argument <code>narg</code> or if this argument is <b>nil</b>.
-<p>
-This is a useful function for mapping strings to C&nbsp;enums.
-(The usual convention in Lua libraries is
-to use strings instead of numbers to select options.)
-<hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>void luaL_checkstack (lua_State *L, int sz, const char *msg);</pre>
-<p>
-Grows the stack size to <code>top + sz</code> elements,
-raising an error if the stack cannot grow to that size.
-<code>msg</code> is an additional text to go into the error message.
-<hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>const char *luaL_checkstring (lua_State *L, int narg);</pre>
-<p>
-Checks whether the function argument <code>narg</code> is a string
-and returns this string.
-<p>
-This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
-so all conversions and caveats of that function apply here.
-<hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>void luaL_checktype (lua_State *L, int narg, int t);</pre>
-<p>
-Checks whether the function argument <code>narg</code> has type <code>t</code>.
-See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>.
-<hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>void *luaL_checkudata (lua_State *L, int narg, const char *tname);</pre>
-<p>
-Checks whether the function argument <code>narg</code> is a userdata
-of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
-<hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p>
-<span class="apii">[-0, +?, <em>m</em>]</span>
-<pre>int luaL_dofile (lua_State *L, const char *filename);</pre>
-<p>
-Loads and runs the given file.
-It is defined as the following macro:
-<pre>
-     (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0))
-</pre><p>
-It returns 0 if there are no errors
-or 1 in case of errors.
-<hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p>
-<span class="apii">[-0, +?, <em>m</em>]</span>
-<pre>int luaL_dostring (lua_State *L, const char *str);</pre>
-<p>
-Loads and runs the given string.
-It is defined as the following macro:
-<pre>
-     (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0))
-</pre><p>
-It returns 0 if there are no errors
-or 1 in case of errors.
-<hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>int luaL_error (lua_State *L, const char *fmt, ...);</pre>
-<p>
-Raises an error.
-The error message format is given by <code>fmt</code>
-plus any extra arguments,
-following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>.
-It also adds at the beginning of the message the file name and
-the line number where the error occurred,
-if this information is available.
-<p>
-This function never returns,
-but it is an idiom to use it in C&nbsp;functions
-as <code>return luaL_error(<em>args</em>)</code>.
-<hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p>
-<span class="apii">[-0, +(0|1), <em>m</em>]</span>
-<pre>int luaL_getmetafield (lua_State *L, int obj, const char *e);</pre>
-<p>
-Pushes onto the stack the field <code>e</code> from the metatable
-of the object at index <code>obj</code>.
-If the object does not have a metatable,
-or if the metatable does not have this field,
-returns 0 and pushes nothing.
-<hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p>
-<span class="apii">[-0, +1, <em>-</em>]</span>
-<pre>void luaL_getmetatable (lua_State *L, const char *tname);</pre>
-<p>
-Pushes onto the stack the metatable associated with name <code>tname</code>
-in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
-<hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>const char *luaL_gsub (lua_State *L,
-                       const char *s,
-                       const char *p,
-                       const char *r);</pre>
-<p>
-Creates a copy of string <code>s</code> by replacing
-any occurrence of the string <code>p</code>
-with the string <code>r</code>.
-Pushes the resulting string on the stack and returns it.
-<hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>int luaL_loadbuffer (lua_State *L,
-                     const char *buff,
-                     size_t sz,
-                     const char *name);</pre>
-<p>
-Loads a buffer as a Lua chunk.
-This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the
-buffer pointed to by <code>buff</code> with size <code>sz</code>.
-<p>
-This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
-<code>name</code> is the chunk name,
-used for debug information and error messages.
-<hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>int luaL_loadfile (lua_State *L, const char *filename);</pre>
-<p>
-Loads a file as a Lua chunk.
-This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the file
-named <code>filename</code>.
-If <code>filename</code> is <code>NULL</code>,
-then it loads from the standard input.
-The first line in the file is ignored if it starts with a <code>#</code>.
-<p>
-This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>,
-but it has an extra error code <a name="pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a>
-if it cannot open/read the file.
-<p>
-As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
-it does not run it.
-<hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>int luaL_loadstring (lua_State *L, const char *s);</pre>
-<p>
-Loads a string as a Lua chunk.
-This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in
-the zero-terminated string <code>s</code>.
-<p>
-This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
-<p>
-Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
-it does not run it.
-<hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>int luaL_newmetatable (lua_State *L, const char *tname);</pre>
-<p>
-If the registry already has the key <code>tname</code>,
-returns 0.
-Otherwise,
-creates a new table to be used as a metatable for userdata,
-adds it to the registry with key <code>tname</code>,
-and returns 1.
-<p>
-In both cases pushes onto the stack the final value associated
-with <code>tname</code> in the registry.
-<hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>lua_State *luaL_newstate (void);</pre>
-<p>
-Creates a new Lua state.
-It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an
-allocator based on the standard&nbsp;C <code>realloc</code> function
-and then sets a panic function (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>) that prints
-an error message to the standard error output in case of fatal
-errors.
-<p>
-Returns the new state,
-or <code>NULL</code> if there is a memory allocation error.
-<hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p>
-<span class="apii">[-0, +0, <em>m</em>]</span>
-<pre>void luaL_openlibs (lua_State *L);</pre>
-<p>
-Opens all standard Lua libraries into the given state.
-<hr><h3><a name="luaL_optint"><code>luaL_optint</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>int luaL_optint (lua_State *L, int narg, int d);</pre>
-<p>
-If the function argument <code>narg</code> is a number,
-returns this number cast to an <code>int</code>.
-If this argument is absent or is <b>nil</b>,
-returns <code>d</code>.
-Otherwise, raises an error.
-<hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>lua_Integer luaL_optinteger (lua_State *L,
-                             int narg,
-                             lua_Integer d);</pre>
-<p>
-If the function argument <code>narg</code> is a number,
-returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>.
-If this argument is absent or is <b>nil</b>,
-returns <code>d</code>.
-Otherwise, raises an error.
-<hr><h3><a name="luaL_optlong"><code>luaL_optlong</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>long luaL_optlong (lua_State *L, int narg, long d);</pre>
-<p>
-If the function argument <code>narg</code> is a number,
-returns this number cast to a <code>long</code>.
-If this argument is absent or is <b>nil</b>,
-returns <code>d</code>.
-Otherwise, raises an error.
-<hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>const char *luaL_optlstring (lua_State *L,
-                             int narg,
-                             const char *d,
-                             size_t *l);</pre>
-<p>
-If the function argument <code>narg</code> is a string,
-returns this string.
-If this argument is absent or is <b>nil</b>,
-returns <code>d</code>.
-Otherwise, raises an error.
-<p>
-If <code>l</code> is not <code>NULL</code>,
-fills the position <code>*l</code> with the results's length.
-<hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>lua_Number luaL_optnumber (lua_State *L, int narg, lua_Number d);</pre>
-<p>
-If the function argument <code>narg</code> is a number,
-returns this number.
-If this argument is absent or is <b>nil</b>,
-returns <code>d</code>.
-Otherwise, raises an error.
-<hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>const char *luaL_optstring (lua_State *L,
-                            int narg,
-                            const char *d);</pre>
-<p>
-If the function argument <code>narg</code> is a string,
-returns this string.
-If this argument is absent or is <b>nil</b>,
-returns <code>d</code>.
-Otherwise, raises an error.
-<hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>char *luaL_prepbuffer (luaL_Buffer *B);</pre>
-<p>
-Returns an address to a space of size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a>
-where you can copy a string to be added to buffer <code>B</code>
-(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
-After copying the string into this space you must call
-<a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add 
-it to the buffer.
-<hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p>
-<span class="apii">[-?, +1, <em>m</em>]</span>
-<pre>void luaL_pushresult (luaL_Buffer *B);</pre>
-<p>
-Finishes the use of buffer <code>B</code> leaving the final string on
-the top of the stack.
-<hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p>
-<span class="apii">[-1, +0, <em>m</em>]</span>
-<pre>int luaL_ref (lua_State *L, int t);</pre>
-<p>
-Creates and returns a <em>reference</em>,
-in the table at index <code>t</code>,
-for the object at the top of the stack (and pops the object).
-<p>
-A reference is a unique integer key.
-As long as you do not manually add integer keys into table <code>t</code>,
-<a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns.
-You can retrieve an object referred by reference <code>r</code>
-by calling <code>lua_rawgeti(L, t, r)</code>.
-Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object.
-<p>
-If the object at the top of the stack is <b>nil</b>,
-<a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>.
-The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different
-from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>.
-<hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3>
-<pre>typedef struct luaL_Reg {
-  const char *name;
-  lua_CFunction func;
-} luaL_Reg;</pre>
-<p>
-Type for arrays of functions to be registered by
-<a href="#luaL_register"><code>luaL_register</code></a>.
-<code>name</code> is the function name and <code>func</code> is a pointer to
-the function.
-Any array of <a href="#luaL_Reg"><code>luaL_Reg</code></a> must end with an sentinel entry
-in which both <code>name</code> and <code>func</code> are <code>NULL</code>.
-<hr><h3><a name="luaL_register"><code>luaL_register</code></a></h3><p>
-<span class="apii">[-(0|1), +1, <em>m</em>]</span>
-<pre>void luaL_register (lua_State *L,
-                    const char *libname,
-                    const luaL_Reg *l);</pre>
-<p>
-Opens a library.
-<p>
-When called with <code>libname</code> equal to <code>NULL</code>,
-it simply registers all functions in the list <code>l</code>
-(see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack.
-<p>
-When called with a non-null <code>libname</code>,
-<code>luaL_register</code> creates a new table <code>t</code>,
-sets it as the value of the global variable <code>libname</code>,
-sets it as the value of <code>package.loaded[libname]</code>,
-and registers on it all functions in the list <code>l</code>.
-If there is a table in <code>package.loaded[libname]</code> or in
-variable <code>libname</code>,
-reuses this table instead of creating a new one.
-<p>
-In any case the function leaves the table
-on the top of the stack.
-<hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>const char *luaL_typename (lua_State *L, int index);</pre>
-<p>
-Returns the name of the type of the value at the given index.
-<hr><h3><a name="luaL_typerror"><code>luaL_typerror</code></a></h3><p>
-<span class="apii">[-0, +0, <em>v</em>]</span>
-<pre>int luaL_typerror (lua_State *L, int narg, const char *tname);</pre>
-<p>
-Generates an error with a message like the following:
-<pre>
-     <em>location</em>: bad argument <em>narg</em> to '<em>func</em>' (<em>tname</em> expected, got <em>rt</em>)
-</pre><p>
-where <code><em>location</em></code> is produced by <a href="#luaL_where"><code>luaL_where</code></a>,
-<code><em>func</em></code> is the name of the current function,
-and <code><em>rt</em></code> is the type name of the actual argument.
-<hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p>
-<span class="apii">[-0, +0, <em>-</em>]</span>
-<pre>void luaL_unref (lua_State *L, int t, int ref);</pre>
-<p>
-Releases reference <code>ref</code> from the table at index <code>t</code>
-(see <a href="#luaL_ref"><code>luaL_ref</code></a>).
-The entry is removed from the table,
-so that the referred object can be collected.
-The reference <code>ref</code> is also freed to be used again.
-<p>
-If <code>ref</code> is <a href="#pdf-LUA_NOREF"><code>LUA_NOREF</code></a> or <a href="#pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>,
-<a href="#luaL_unref"><code>luaL_unref</code></a> does nothing.
-<hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p>
-<span class="apii">[-0, +1, <em>m</em>]</span>
-<pre>void luaL_where (lua_State *L, int lvl);</pre>
-<p>
-Pushes onto the stack a string identifying the current position
-of the control at level <code>lvl</code> in the call stack.
-Typically this string has the following format:
-<pre>
-     <em>chunkname</em>:<em>currentline</em>:
-</pre><p>
-Level&nbsp;0 is the running function,
-level&nbsp;1 is the function that called the running function,
-etc.
-<p>
-This function is used to build a prefix for error messages.
-<h1>5 - <a name="5">Standard Libraries</a></h1>
-<p>
-The standard Lua libraries provide useful functions
-that are implemented directly through the C&nbsp;API.
-Some of these functions provide essential services to the language
-(e.g., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>);
-others provide access to "outside" services (e.g., I/O);
-and others could be implemented in Lua itself,
-but are quite useful or have critical performance requirements that
-deserve an implementation in C (e.g., <a href="#pdf-table.sort"><code>table.sort</code></a>).
-<p>
-All libraries are implemented through the official C&nbsp;API
-and are provided as separate C&nbsp;modules.
-Currently, Lua has the following standard libraries:
-<ul>
-<li>basic library,</li> which includes the coroutine sub-library;
-<li>package library;</li>
-<li>string manipulation;</li>
-<li>table manipulation;</li>
-<li>mathematical functions (sin, log, etc.);</li>
-<li>input and output;</li>
-<li>operating system facilities;</li>
-<li>debug facilities.</li>
-</ul><p>
-Except for the basic and package libraries,
-each library provides all its functions as fields of a global table
-or as methods of its objects.
-<p>
-To have access to these libraries,
-the C&nbsp;host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function,
-which opens all standard libraries.
-Alternatively,
-it can open them individually by calling
-<a name="pdf-luaopen_base"><code>luaopen_base</code></a> (for the basic library),
-<a name="pdf-luaopen_package"><code>luaopen_package</code></a> (for the package library),
-<a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library),
-<a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library),
-<a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library),
-<a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library),
-<a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the Operating System library),
-and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library).
-These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a>
-and should not be called directly:
-you must call them like any other Lua C&nbsp;function,
-e.g., by using <a href="#lua_call"><code>lua_call</code></a>.
-<h2>5.1 - <a name="5.1">Basic Functions</a></h2>
-<p>
-The basic library provides some core functions to Lua.
-If you do not include this library in your application,
-you should check carefully whether you need to provide 
-implementations for some of its facilities.
-<p>
-<hr><h3><a name="pdf-assert"><code>assert (v [, message])</code></a></h3>
-Issues an  error when
-the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>);
-otherwise, returns all its arguments.
-<code>message</code> is an error message;
-when absent, it defaults to "assertion failed!"
-<p>
-<hr><h3><a name="pdf-collectgarbage"><code>collectgarbage (opt [, arg])</code></a></h3>
-<p>
-This function is a generic interface to the garbage collector.
-It performs different functions according to its first argument, <code>opt</code>:
-<ul>
-<li><b>"stop":</b>
-stops the garbage collector.
-</li>
-<li><b>"restart":</b>
-restarts the garbage collector.
-</li>
-<li><b>"collect":</b>
-performs a full garbage-collection cycle.
-</li>
-<li><b>"count":</b>
-returns the total memory in use by Lua (in Kbytes).
-</li>
-<li><b>"step":</b>
-performs a garbage-collection step.
-The step "size" is controlled by <code>arg</code>
-(larger values mean more steps) in a non-specified way.
-If you want to control the step size
-you must experimentally tune the value of <code>arg</code>.
-Returns <b>true</b> if the step finished a collection cycle.
-</li>
-<li><b>"setpause":</b>
-sets <code>arg</code> as the new value for the <em>pause</em> of
-the collector (see <a href="#2.10">&sect;2.10</a>).
-Returns the previous value for <em>pause</em>.
-</li>
-<li><b>"setstepmul":</b>
-sets <code>arg</code> as the new value for the <em>step multiplier</em> of
-the collector (see <a href="#2.10">&sect;2.10</a>).
-Returns the previous value for <em>step</em>.
-</li>
-</ul>
-<p>
-<hr><h3><a name="pdf-dofile"><code>dofile (filename)</code></a></h3>
-Opens the named file and executes its contents as a Lua chunk.
-When called without arguments,
-<code>dofile</code> executes the contents of the standard input (<code>stdin</code>).
-Returns all values returned by the chunk.
-In case of errors, <code>dofile</code> propagates the error
-to its caller (that is, <code>dofile</code> does not run in protected mode).
-<p>
-<hr><h3><a name="pdf-error"><code>error (message [, level])</code></a></h3>
-Terminates the last protected function called
-and returns <code>message</code> as the error message.
-Function <code>error</code> never returns.
-<p>
-Usually, <code>error</code> adds some information about the error position
-at the beginning of the message.
-The <code>level</code> argument specifies how to get the error position.
-With level&nbsp;1 (the default), the error position is where the
-<code>error</code> function was called.
-Level&nbsp;2 points the error to where the function
-that called <code>error</code> was called; and so on.
-Passing a level&nbsp;0 avoids the addition of error position information
-to the message.
-<p>
-<hr><h3><a name="pdf-_G"><code>_G</code></a></h3>
-A global variable (not a function) that
-holds the global environment (that is, <code>_G._G = _G</code>).
-Lua itself does not use this variable;
-changing its value does not affect any environment,
-nor vice-versa.
-(Use <a href="#pdf-setfenv"><code>setfenv</code></a> to change environments.)
-<p>
-<hr><h3><a name="pdf-getfenv"><code>getfenv ([f])</code></a></h3>
-Returns the current environment in use by the function.
-<code>f</code> can be a Lua function or a number
-that specifies the function at that stack level:
-Level&nbsp;1 is the function calling <code>getfenv</code>.
-If the given function is not a Lua function,
-or if <code>f</code> is 0,
-<code>getfenv</code> returns the global environment.
-The default for <code>f</code> is 1.
-<p>
-<hr><h3><a name="pdf-getmetatable"><code>getmetatable (object)</code></a></h3>
-<p>
-If <code>object</code> does not have a metatable, returns <b>nil</b>.
-Otherwise,
-if the object's metatable has a <code>"__metatable"</code> field,
-returns the associated value.
-Otherwise, returns the metatable of the given object.
-<p>
-<hr><h3><a name="pdf-ipairs"><code>ipairs (t)</code></a></h3>
-<p>
-Returns three values: an iterator function, the table <code>t</code>, and 0,
-so that the construction
-<pre>
-     for i,v in ipairs(t) do <em>body</em> end
-</pre><p>
-will iterate over the pairs (<code>1,t[1]</code>), (<code>2,t[2]</code>), &middot;&middot;&middot;,
-up to the first integer key absent from the table.
-<p>
-<hr><h3><a name="pdf-load"><code>load (func [, chunkname])</code></a></h3>
-<p>
-Loads a chunk using function <code>func</code> to get its pieces.
-Each call to <code>func</code> must return a string that concatenates
-with previous results.
-A return of an empty string, <b>nil</b>, or no value signals the end of the chunk.
-<p>
-If there are no errors, 
-returns the compiled chunk as a function;
-otherwise, returns <b>nil</b> plus the error message.
-The environment of the returned function is the global environment.
-<p>
-<code>chunkname</code> is used as the chunk name for error messages
-and debug information.
-When absent,
-it defaults to "<code>=(load)</code>".
-<p>
-<hr><h3><a name="pdf-loadfile"><code>loadfile ([filename])</code></a></h3>
-<p>
-Similar to <a href="#pdf-load"><code>load</code></a>,
-but gets the chunk from file <code>filename</code>
-or from the standard input,
-if no file name is given.
-<p>
-<hr><h3><a name="pdf-loadstring"><code>loadstring (string [, chunkname])</code></a></h3>
-<p>
-Similar to <a href="#pdf-load"><code>load</code></a>,
-but gets the chunk from the given string.
-<p>
-To load and run a given string, use the idiom
-<pre>
-     assert(loadstring(s))()
-</pre>
-<p>
-When absent,
-<code>chunkname</code> defaults to the given string.
-<p>
-<hr><h3><a name="pdf-next"><code>next (table [, index])</code></a></h3>
-<p>
-Allows a program to traverse all fields of a table.
-Its first argument is a table and its second argument
-is an index in this table.
-<code>next</code> returns the next index of the table
-and its associated value.
-When called with <b>nil</b> as its second argument,
-<code>next</code> returns an initial index
-and its associated value.
-When called with the last index,
-or with <b>nil</b> in an empty table,
-<code>next</code> returns <b>nil</b>.
-If the second argument is absent, then it is interpreted as <b>nil</b>.
-In particular,
-you can use <code>next(t)</code> to check whether a table is empty.
-<p>
-The order in which the indices are enumerated is not specified,
-<em>even for numeric indices</em>.
-(To traverse a table in numeric order,
-use a numerical <b>for</b> or the <a href="#pdf-ipairs"><code>ipairs</code></a> function.)
-<p>
-The behavior of <code>next</code> is <em>undefined</em> if,
-during the traversal,
-you assign any value to a non-existent field in the table.
-You may however modify existing fields.
-In particular, you may clear existing fields.
-<p>
-<hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3>
-<p>
-Returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>,
-so that the construction
-<pre>
-     for k,v in pairs(t) do <em>body</em> end
-</pre><p>
-will iterate over all key&ndash;value pairs of table <code>t</code>.
-<p>
-See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying
-the table during its traversal.
-<p>
-<hr><h3><a name="pdf-pcall"><code>pcall (f, arg1, &middot;&middot;&middot;)</code></a></h3>
-<p>
-Calls function <code>f</code> with
-the given arguments in <em>protected mode</em>.
-This means that any error inside&nbsp;<code>f</code> is not propagated;
-instead, <code>pcall</code> catches the error
-and returns a status code.
-Its first result is the status code (a boolean),
-which is true if the call succeeds without errors.
-In such case, <code>pcall</code> also returns all results from the call,
-after this first result.
-In case of any error, <code>pcall</code> returns <b>false</b> plus the error message.
-<p>
-<hr><h3><a name="pdf-print"><code>print (&middot;&middot;&middot;)</code></a></h3>
-Receives any number of arguments,
-and prints their values to <code>stdout</code>,
-using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert them to strings.
-<code>print</code> is not intended for formatted output,
-but only as a quick way to show a value,
-typically for debugging.
-For formatted output, use <a href="#pdf-string.format"><code>string.format</code></a>.
-<p>
-<hr><h3><a name="pdf-rawequal"><code>rawequal (v1, v2)</code></a></h3>
-Checks whether <code>v1</code> is equal to <code>v2</code>,
-without invoking any metamethod.
-Returns a boolean.
-<p>
-<hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3>
-Gets the real value of <code>table[index]</code>,
-without invoking any metamethod.
-<code>table</code> must be a table;
-<code>index</code> may be any value.
-<p>
-<hr><h3><a name="pdf-rawset"><code>rawset (table, index, value)</code></a></h3>
-Sets the real value of <code>table[index]</code> to <code>value</code>,
-without invoking any metamethod.
-<code>table</code> must be a table,
-<code>index</code> any value different from <b>nil</b>,
-and <code>value</code> any Lua value.
-<p>
-This function returns <code>table</code>.
-<p>
-<hr><h3><a name="pdf-select"><code>select (index, &middot;&middot;&middot;)</code></a></h3>
-<p>
-If <code>index</code> is a number,
-returns all arguments after argument number <code>index</code>.
-Otherwise, <code>index</code> must be the string <code>"#"</code>,
-and <code>select</code> returns the total number of extra arguments it received.
-<p>
-<hr><h3><a name="pdf-setfenv"><code>setfenv (f, table)</code></a></h3>
-<p>
-Sets the environment to be used by the given function.
-<code>f</code> can be a Lua function or a number
-that specifies the function at that stack level:
-Level&nbsp;1 is the function calling <code>setfenv</code>.
-<code>setfenv</code> returns the given function.
-<p>
-As a special case, when <code>f</code> is 0 <code>setfenv</code> changes
-the environment of the running thread.
-In this case, <code>setfenv</code> returns no values.
-<p>
-<hr><h3><a name="pdf-setmetatable"><code>setmetatable (table, metatable)</code></a></h3>
-<p>
-Sets the metatable for the given table.
-(You cannot change the metatable of other types from Lua, only from&nbsp;C.)
-If <code>metatable</code> is <b>nil</b>,
-removes the metatable of the given table.
-If the original metatable has a <code>"__metatable"</code> field,
-raises an error.
-<p>
-This function returns <code>table</code>.
-<p>
-<hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3>
-Tries to convert its argument to a number.
-If the argument is already a number or a string convertible
-to a number, then <code>tonumber</code> returns this number;
-otherwise, it returns <b>nil</b>.
-<p>
-An optional argument specifies the base to interpret the numeral.
-The base may be any integer between 2 and 36, inclusive.
-In bases above&nbsp;10, the letter '<code>A</code>' (in either upper or lower case)
-represents&nbsp;10, '<code>B</code>' represents&nbsp;11, and so forth,
-with '<code>Z</code>' representing 35.
-In base 10 (the default), the number can have a decimal part,
-as well as an optional exponent part (see <a href="#2.1">&sect;2.1</a>).
-In other bases, only unsigned integers are accepted.
-<p>
-<hr><h3><a name="pdf-tostring"><code>tostring (e)</code></a></h3>
-Receives an argument of any type and
-converts it to a string in a reasonable format.
-For complete control of how numbers are converted,
-use <a href="#pdf-string.format"><code>string.format</code></a>.
-<p>
-If the metatable of <code>e</code> has a <code>"__tostring"</code> field,
-then <code>tostring</code> calls the corresponding value
-with <code>e</code> as argument,
-and uses the result of the call as its result.
-<p>
-<hr><h3><a name="pdf-type"><code>type (v)</code></a></h3>
-Returns the type of its only argument, coded as a string.
-The possible results of this function are
-"<code>nil</code>" (a string, not the value <b>nil</b>),
-"<code>number</code>",
-"<code>string</code>",
-"<code>boolean</code>",
-"<code>table</code>",
-"<code>function</code>",
-"<code>thread</code>",
-and "<code>userdata</code>".
-<p>
-<hr><h3><a name="pdf-unpack"><code>unpack (list [, i [, j]])</code></a></h3>
-Returns the elements from the given table.
-This function is equivalent to
-<pre>
-     return list[i], list[i+1], &middot;&middot;&middot;, list[j]
-</pre><p>
-except that the above code can be written only for a fixed number
-of elements.
-By default, <code>i</code> is&nbsp;1 and <code>j</code> is the length of the list,
-as defined by the length operator (see <a href="#2.5.5">&sect;2.5.5</a>).
-<p>
-<hr><h3><a name="pdf-_VERSION"><code>_VERSION</code></a></h3>
-A global variable (not a function) that
-holds a string containing the current interpreter version.
-The current contents of this variable is "<code>Lua 5.1</code>".
-<p>
-<hr><h3><a name="pdf-xpcall"><code>xpcall (f, err)</code></a></h3>
-<p>
-This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>,
-except that you can set a new error handler.
-<p>
-<code>xpcall</code> calls function <code>f</code> in protected mode,
-using <code>err</code> as the error handler.
-Any error inside <code>f</code> is not propagated;
-instead, <code>xpcall</code> catches the error,
-calls the <code>err</code> function with the original error object,
-and returns a status code.
-Its first result is the status code (a boolean),
-which is true if the call succeeds without errors.
-In this case, <code>xpcall</code> also returns all results from the call,
-after this first result.
-In case of any error,
-<code>xpcall</code> returns <b>false</b> plus the result from <code>err</code>.
-<h2>5.2 - <a name="5.2">Coroutine Manipulation</a></h2>
-<p>
-The operations related to coroutines comprise a sub-library of
-the basic library and come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>.
-See <a href="#2.11">&sect;2.11</a> for a general description of coroutines.
-<p>
-<hr><h3><a name="pdf-coroutine.create"><code>coroutine.create (f)</code></a></h3>
-<p>
-Creates a new coroutine, with body <code>f</code>.
-<code>f</code> must be a Lua function.
-Returns this new coroutine,
-an object with type <code>"thread"</code>.
-<p>
-<hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, &middot;&middot;&middot;])</code></a></h3>
-<p>
-Starts or continues the execution of coroutine <code>co</code>.
-The first time you resume a coroutine,
-it starts running its body.
-The values <code>val1</code>, &middot;&middot;&middot; are passed
-as the arguments to the body function.
-If the coroutine has yielded,
-<code>resume</code> restarts it;
-the values <code>val1</code>, &middot;&middot;&middot; are passed
-as the results from the yield.
-<p>
-If the coroutine runs without any errors,
-<code>resume</code> returns <b>true</b> plus any values passed to <code>yield</code>
-(if the coroutine yields) or any values returned by the body function
-(if the coroutine terminates).
-If there is any error,
-<code>resume</code> returns <b>false</b> plus the error message.
-<p>
-<hr><h3><a name="pdf-coroutine.running"><code>coroutine.running ()</code></a></h3>
-<p>
-Returns the running coroutine,
-or <b>nil</b> when called by the main thread.
-<p>
-<hr><h3><a name="pdf-coroutine.status"><code>coroutine.status (co)</code></a></h3>
-<p>
-Returns the status of coroutine <code>co</code>, as a string:
-<code>"running"</code>,
-if the coroutine is running (that is, it called <code>status</code>);
-<code>"suspended"</code>, if the coroutine is suspended in a call to <code>yield</code>,
-or if it has not started running yet;
-<code>"normal"</code> if the coroutine is active but not running
-(that is, it has resumed another coroutine);
-and <code>"dead"</code> if the coroutine has finished its body function,
-or if it has stopped with an error.
-<p>
-<hr><h3><a name="pdf-coroutine.wrap"><code>coroutine.wrap (f)</code></a></h3>
-<p>
-Creates a new coroutine, with body <code>f</code>.
-<code>f</code> must be a Lua function.
-Returns a function that resumes the coroutine each time it is called.
-Any arguments passed to the function behave as the
-extra arguments to <code>resume</code>.
-Returns the same values returned by <code>resume</code>,
-except the first boolean.
-In case of error, propagates the error.
-<p>
-<hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (&middot;&middot;&middot;)</code></a></h3>
-<p>
-Suspends the execution of the calling coroutine.
-The coroutine cannot be running a C&nbsp;function,
-a metamethod, or an iterator.
-Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>.
-<h2>5.3 - <a name="5.3">Modules</a></h2>
-<p>
-The package library provides basic
-facilities for loading and building modules in Lua.
-It exports two of its functions directly in the global environment:
-<a href="#pdf-require"><code>require</code></a> and <a href="#pdf-module"><code>module</code></a>.
-Everything else is exported in a table <a name="pdf-package"><code>package</code></a>.
-<p>
-<hr><h3><a name="pdf-module"><code>module (name [, &middot;&middot;&middot;])</code></a></h3>
-<p>
-Creates a module.
-If there is a table in <code>package.loaded[name]</code>,
-this table is the module.
-Otherwise, if there is a global table <code>t</code> with the given name,
-this table is the module.
-Otherwise creates a new table <code>t</code> and
-sets it as the value of the global <code>name</code> and
-the value of <code>package.loaded[name]</code>.
-This function also initializes <code>t._NAME</code> with the given name,
-<code>t._M</code> with the module (<code>t</code> itself),
-and <code>t._PACKAGE</code> with the package name
-(the full module name minus last component; see below).
-Finally, <code>module</code> sets <code>t</code> as the new environment
-of the current function and the new value of <code>package.loaded[name]</code>,
-so that <a href="#pdf-require"><code>require</code></a> returns <code>t</code>.
-<p>
-If <code>name</code> is a compound name
-(that is, one with components separated by dots),
-<code>module</code> creates (or reuses, if they already exist)
-tables for each component.
-For instance, if <code>name</code> is <code>a.b.c</code>,
-then <code>module</code> stores the module table in field <code>c</code> of
-field <code>b</code> of global <code>a</code>.
-<p>
-This function can receive optional <em>options</em> after
-the module name,
-where each option is a function to be applied over the module.
-<p>
-<hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3>
-<p>
-Loads the given module.
-The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table
-to determine whether <code>modname</code> is already loaded.
-If it is, then <code>require</code> returns the value stored
-at <code>package.loaded[modname]</code>.
-Otherwise, it tries to find a <em>loader</em> for the module.
-<p>
-To find a loader,
-<code>require</code> is guided by the <a href="#pdf-package.loaders"><code>package.loaders</code></a> array.
-By changing this array,
-we can change how <code>require</code> looks for a module.
-The following explanation is based on the default configuration
-for <a href="#pdf-package.loaders"><code>package.loaders</code></a>.
-<p>
-First <code>require</code> queries <code>package.preload[modname]</code>.
-If it has a value,
-this value (which should be a function) is the loader.
-Otherwise <code>require</code> searches for a Lua loader using the
-path stored in <a href="#pdf-package.path"><code>package.path</code></a>.
-If that also fails, it searches for a C&nbsp;loader using the
-path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
-If that also fails,
-it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.loaders"><code>package.loaders</code></a>).
-<p>
-Once a loader is found,
-<code>require</code> calls the loader with a single argument, <code>modname</code>.
-If the loader returns any value,
-<code>require</code> assigns the returned value to <code>package.loaded[modname]</code>.
-If the loader returns no value and
-has not assigned any value to <code>package.loaded[modname]</code>,
-then <code>require</code> assigns <b>true</b> to this entry.
-In any case, <code>require</code> returns the
-final value of <code>package.loaded[modname]</code>.
-<p>
-If there is any error loading or running the module,
-or if it cannot find any loader for the module,
-then <code>require</code> signals an error. 
-<p>
-<hr><h3><a name="pdf-package.cpath"><code>package.cpath</code></a></h3>
-<p>
-The path used by <a href="#pdf-require"><code>require</code></a> to search for a C&nbsp;loader.
-<p>
-Lua initializes the C&nbsp;path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way
-it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>,
-using the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a>
-or a default path defined in <code>luaconf.h</code>.
-<p>
-<hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3>
-<p>
-A table used by <a href="#pdf-require"><code>require</code></a> to control which
-modules are already loaded.
-When you require a module <code>modname</code> and
-<code>package.loaded[modname]</code> is not false,
-<a href="#pdf-require"><code>require</code></a> simply returns the value stored there.
-<p>
-<hr><h3><a name="pdf-package.loaders"><code>package.loaders</code></a></h3>
-<p>
-A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules.
-<p>
-Each entry in this table is a <em>searcher function</em>.
-When looking for a module,
-<a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order,
-with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its
-sole parameter.
-The function can return another function (the module <em>loader</em>)
-or a string explaining why it did not find that module
-(or <b>nil</b> if it has nothing to say).
-Lua initializes this table with four functions.
-<p>
-The first searcher simply looks for a loader in the
-<a href="#pdf-package.preload"><code>package.preload</code></a> table.
-<p>
-The second searcher looks for a loader as a Lua library,
-using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>.
-A path is a sequence of <em>templates</em> separated by semicolons.
-For each template,
-the searcher will change each interrogation
-mark in the template by <code>filename</code>,
-which is the module name with each dot replaced by a
-"directory separator" (such as "<code>/</code>" in Unix);
-then it will try to open the resulting file name.
-So, for instance, if the Lua path is the string
-<pre>
-     "./?.lua;./?.lc;/usr/local/?/init.lua"
-</pre><p>
-the search for a Lua file for module <code>foo</code>
-will try to open the files
-<code>./foo.lua</code>, <code>./foo.lc</code>, and
-<code>/usr/local/foo/init.lua</code>, in that order.
-<p>
-The third searcher looks for a loader as a C&nbsp;library,
-using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
-For instance,
-if the C&nbsp;path is the string
-<pre>
-     "./?.so;./?.dll;/usr/local/?/init.so"
-</pre><p>
-the searcher for module <code>foo</code>
-will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>,
-and <code>/usr/local/foo/init.so</code>, in that order.
-Once it finds a C&nbsp;library,
-this searcher first uses a dynamic link facility to link the
-application with the library.
-Then it tries to find a C&nbsp;function inside the library to
-be used as the loader.
-The name of this C&nbsp;function is the string "<code>luaopen_</code>"
-concatenated with a copy of the module name where each dot
-is replaced by an underscore.
-Moreover, if the module name has a hyphen,
-its prefix up to (and including) the first hyphen is removed.
-For instance, if the module name is <code>a.v1-b.c</code>,
-the function name will be <code>luaopen_b_c</code>.
-<p>
-The fourth searcher tries an <em>all-in-one loader</em>.
-It searches the C&nbsp;path for a library for
-the root name of the given module.
-For instance, when requiring <code>a.b.c</code>,
-it will search for a C&nbsp;library for <code>a</code>.
-If found, it looks into it for an open function for
-the submodule;
-in our example, that would be <code>luaopen_a_b_c</code>.
-With this facility, a package can pack several C&nbsp;submodules
-into one single library,
-with each submodule keeping its original open function.
-<p>
-<hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3>
-<p>
-Dynamically links the host program with the C&nbsp;library <code>libname</code>.
-Inside this library, looks for a function <code>funcname</code>
-and returns this function as a C&nbsp;function.
-(So, <code>funcname</code> must follow the protocol (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>)).
-<p>
-This is a low-level function.
-It completely bypasses the package and module system.
-Unlike <a href="#pdf-require"><code>require</code></a>,
-it does not perform any path searching and
-does not automatically adds extensions.
-<code>libname</code> must be the complete file name of the C&nbsp;library,
-including if necessary a path and extension.
-<code>funcname</code> must be the exact name exported by the C&nbsp;library
-(which may depend on the C&nbsp;compiler and linker used).
-<p>
-This function is not supported by ANSI C.
-As such, it is only available on some platforms
-(Windows, Linux, Mac OS X, Solaris, BSD,
-plus other Unix systems that support the <code>dlfcn</code> standard).
-<p>
-<hr><h3><a name="pdf-package.path"><code>package.path</code></a></h3>
-<p>
-The path used by <a href="#pdf-require"><code>require</code></a> to search for a Lua loader.
-<p>
-At start-up, Lua initializes this variable with
-the value of the environment variable <a name="pdf-LUA_PATH"><code>LUA_PATH</code></a> or
-with a default path defined in <code>luaconf.h</code>,
-if the environment variable is not defined.
-Any "<code>;;</code>" in the value of the environment variable
-is replaced by the default path.
-<p>
-<hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3>
-<p>
-A table to store loaders for specific modules
-(see <a href="#pdf-require"><code>require</code></a>).
-<p>
-<hr><h3><a name="pdf-package.seeall"><code>package.seeall (module)</code></a></h3>
-<p>
-Sets a metatable for <code>module</code> with
-its <code>__index</code> field referring to the global environment,
-so that this module inherits values
-from the global environment.
-To be used as an option to function <a href="#pdf-module"><code>module</code></a>.
-<h2>5.4 - <a name="5.4">String Manipulation</a></h2>
-<p>
-This library provides generic functions for string manipulation,
-such as finding and extracting substrings, and pattern matching.
-When indexing a string in Lua, the first character is at position&nbsp;1
-(not at&nbsp;0, as in C).
-Indices are allowed to be negative and are interpreted as indexing backwards,
-from the end of the string.
-Thus, the last character is at position -1, and so on.
-<p>
-The string library provides all its functions inside the table
-<a name="pdf-string"><code>string</code></a>.
-It also sets a metatable for strings
-where the <code>__index</code> field points to the <code>string</code> table.
-Therefore, you can use the string functions in object-oriented style.
-For instance, <code>string.byte(s, i)</code>
-can be written as <code>s:byte(i)</code>.
-<p>
-The string library assumes one-byte character encodings.
-<p>
-<hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3>
-Returns the internal numerical codes of the characters <code>s[i]</code>,
-<code>s[i+1]</code>, &middot;&middot;&middot;, <code>s[j]</code>.
-The default value for <code>i</code> is&nbsp;1;
-the default value for <code>j</code> is&nbsp;<code>i</code>.
-<p>
-Note that numerical codes are not necessarily portable across platforms.
-<p>
-<hr><h3><a name="pdf-string.char"><code>string.char (&middot;&middot;&middot;)</code></a></h3>
-Receives zero or more integers.
-Returns a string with length equal to the number of arguments,
-in which each character has the internal numerical code equal
-to its corresponding argument.
-<p>
-Note that numerical codes are not necessarily portable across platforms.
-<p>
-<hr><h3><a name="pdf-string.dump"><code>string.dump (function)</code></a></h3>
-<p>
-Returns a string containing a binary representation of the given function,
-so that a later <a href="#pdf-loadstring"><code>loadstring</code></a> on this string returns
-a copy of the function.
-<code>function</code> must be a Lua function without upvalues.
-<p>
-<hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3>
-Looks for the first match of
-<code>pattern</code> in the string <code>s</code>.
-If it finds a match, then <code>find</code> returns the indices of&nbsp;<code>s</code>
-where this occurrence starts and ends;
-otherwise, it returns <b>nil</b>.
-A third, optional numerical argument <code>init</code> specifies
-where to start the search;
-its default value is&nbsp;1 and can be negative.
-A value of <b>true</b> as a fourth, optional argument <code>plain</code>
-turns off the pattern matching facilities,
-so the function does a plain "find substring" operation,
-with no characters in <code>pattern</code> being considered "magic".
-Note that if <code>plain</code> is given, then <code>init</code> must be given as well.
-<p>
-If the pattern has captures,
-then in a successful match
-the captured values are also returned,
-after the two indices.
-<p>
-<hr><h3><a name="pdf-string.format"><code>string.format (formatstring, &middot;&middot;&middot;)</code></a></h3>
-Returns a formatted version of its variable number of arguments
-following the description given in its first argument (which must be a string).
-The format string follows the same rules as the <code>printf</code> family of
-standard C&nbsp;functions.
-The only differences are that the options/modifiers
-<code>*</code>, <code>l</code>, <code>L</code>, <code>n</code>, <code>p</code>,
-and <code>h</code> are not supported
-and that there is an extra option, <code>q</code>.
-The <code>q</code> option formats a string in a form suitable to be safely read
-back by the Lua interpreter:
-the string is written between double quotes,
-and all double quotes, newlines, embedded zeros,
-and backslashes in the string
-are correctly escaped when written.
-For instance, the call
-<pre>
-     string.format('%q', 'a string with "quotes" and \n new line')
-</pre><p>
-will produce the string:
-<pre>
-     "a string with \"quotes\" and \
-      new line"
-</pre>
-<p>
-The options <code>c</code>, <code>d</code>, <code>E</code>, <code>e</code>, <code>f</code>,
-<code>g</code>, <code>G</code>, <code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code> all
-expect a number as argument,
-whereas <code>q</code> and <code>s</code> expect a string.
-<p>
-This function does not accept string values
-containing embedded zeros,
-except as arguments to the <code>q</code> option.
-<p>
-<hr><h3><a name="pdf-string.gmatch"><code>string.gmatch (s, pattern)</code></a></h3>
-Returns an iterator function that,
-each time it is called,
-returns the next captures from <code>pattern</code> over string <code>s</code>.
-If <code>pattern</code> specifies no captures,
-then the whole match is produced in each call.
-<p>
-As an example, the following loop
-<pre>
-     s = "hello world from Lua"
-     for w in string.gmatch(s, "%a+") do
-       print(w)
-     end
-</pre><p>
-will iterate over all the words from string <code>s</code>,
-printing one per line.
-The next example collects all pairs <code>key=value</code> from the
-given string into a table:
-<pre>
-     t = {}
-     s = "from=world, to=Lua"
-     for k, v in string.gmatch(s, "(%w+)=(%w+)") do
-       t[k] = v
-     end
-</pre>
-<p>
-For this function, a '<code>^</code>' at the start of a pattern does not
-work as an anchor, as this would prevent the iteration.
-<p>
-<hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3>
-Returns a copy of <code>s</code>
-in which all (or the first <code>n</code>, if given)
-occurrences of the <code>pattern</code> have been
-replaced by a replacement string specified by <code>repl</code>,
-which can be a string, a table, or a function.
-<code>gsub</code> also returns, as its second value,
-the total number of matches that occurred.
-<p>
-If <code>repl</code> is a string, then its value is used for replacement.
-The character&nbsp;<code>%</code> works as an escape character:
-any sequence in <code>repl</code> of the form <code>%<em>n</em></code>,
-with <em>n</em> between 1 and 9,
-stands for the value of the <em>n</em>-th captured substring (see below).
-The sequence <code>%0</code> stands for the whole match.
-The sequence <code>%%</code> stands for a single&nbsp;<code>%</code>.
-<p>
-If <code>repl</code> is a table, then the table is queried for every match,
-using the first capture as the key;
-if the pattern specifies no captures,
-then the whole match is used as the key.
-<p>
-If <code>repl</code> is a function, then this function is called every time a
-match occurs, with all captured substrings passed as arguments,
-in order;
-if the pattern specifies no captures,
-then the whole match is passed as a sole argument.
-<p>
-If the value returned by the table query or by the function call
-is a string or a number,
-then it is used as the replacement string;
-otherwise, if it is <b>false</b> or <b>nil</b>,
-then there is no replacement
-(that is, the original match is kept in the string).
-<p>
-Here are some examples:
-<pre>
-     x = string.gsub("hello world", "(%w+)", "%1 %1")
-     --&gt; x="hello hello world world"
-     
-     x = string.gsub("hello world", "%w+", "%0 %0", 1)
-     --&gt; x="hello hello world"
-     
-     x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
-     --&gt; x="world hello Lua from"
-     
-     x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
-     --&gt; x="home = /home/roberto, user = roberto"
-     
-     x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
-           return loadstring(s)()
-         end)
-     --&gt; x="4+5 = 9"
-     
-     local t = {name="lua", version="5.1"}
-     x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
-     --&gt; x="lua-5.1.tar.gz"
-</pre>
-<p>
-<hr><h3><a name="pdf-string.len"><code>string.len (s)</code></a></h3>
-Receives a string and returns its length.
-The empty string <code>""</code> has length 0.
-Embedded zeros are counted,
-so <code>"a\000bc\000"</code> has length 5.
-<p>
-<hr><h3><a name="pdf-string.lower"><code>string.lower (s)</code></a></h3>
-Receives a string and returns a copy of this string with all
-uppercase letters changed to lowercase.
-All other characters are left unchanged.
-The definition of what an uppercase letter is depends on the current locale.
-<p>
-<hr><h3><a name="pdf-string.match"><code>string.match (s, pattern [, init])</code></a></h3>
-Looks for the first <em>match</em> of
-<code>pattern</code> in the string <code>s</code>.
-If it finds one, then <code>match</code> returns
-the captures from the pattern;
-otherwise it returns <b>nil</b>.
-If <code>pattern</code> specifies no captures,
-then the whole match is returned.
-A third, optional numerical argument <code>init</code> specifies
-where to start the search;
-its default value is&nbsp;1 and can be negative.
-<p>
-<hr><h3><a name="pdf-string.rep"><code>string.rep (s, n)</code></a></h3>
-Returns a string that is the concatenation of <code>n</code> copies of
-the string <code>s</code>.
-<p>
-<hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3>
-Returns a string that is the string <code>s</code> reversed.
-<p>
-<hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3>
-Returns the substring of <code>s</code> that
-starts at <code>i</code>  and continues until <code>j</code>;
-<code>i</code> and <code>j</code> can be negative.
-If <code>j</code> is absent, then it is assumed to be equal to -1
-(which is the same as the string length).
-In particular,
-the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code>
-with length <code>j</code>,
-and <code>string.sub(s, -i)</code> returns a suffix of <code>s</code>
-with length <code>i</code>.
-<p>
-<hr><h3><a name="pdf-string.upper"><code>string.upper (s)</code></a></h3>
-Receives a string and returns a copy of this string with all
-lowercase letters changed to uppercase.
-All other characters are left unchanged.
-The definition of what a lowercase letter is depends on the current locale.
-<h3>5.4.1 - <a name="5.4.1">Patterns</a></h3>
-<h4>Character Class:</h4><p>
-A <em>character class</em> is used to represent a set of characters.
-The following combinations are allowed in describing a character class:
-<ul>
-<li><b><em>x</em>:</b>
-(where <em>x</em> is not one of the <em>magic characters</em>
-<code>^$()%.[]*+-?</code>)
-represents the character <em>x</em> itself.
-</li>
-<li><b><code>.</code>:</b> (a dot) represents all characters.</li>
-<li><b><code>%a</code>:</b> represents all letters.</li>
-<li><b><code>%c</code>:</b> represents all control characters.</li>
-<li><b><code>%d</code>:</b> represents all digits.</li>
-<li><b><code>%l</code>:</b> represents all lowercase letters.</li>
-<li><b><code>%p</code>:</b> represents all punctuation characters.</li>
-<li><b><code>%s</code>:</b> represents all space characters.</li>
-<li><b><code>%u</code>:</b> represents all uppercase letters.</li>
-<li><b><code>%w</code>:</b> represents all alphanumeric characters.</li>
-<li><b><code>%x</code>:</b> represents all hexadecimal digits.</li>
-<li><b><code>%z</code>:</b> represents the character with representation 0.</li>
-<li><b><code>%<em>x</em></code>:</b> (where <em>x</em> is any non-alphanumeric character)
-represents the character <em>x</em>.
-This is the standard way to escape the magic characters.
-Any punctuation character (even the non magic)
-can be preceded by a '<code>%</code>'
-when used to represent itself in a pattern.
-</li>
-<li><b><code>[<em>set</em>]</code>:</b>
-represents the class which is the union of all
-characters in <em>set</em>.
-A range of characters can be specified by
-separating the end characters of the range with a '<code>-</code>'.
-All classes <code>%</code><em>x</em> described above can also be used as
-components in <em>set</em>.
-All other characters in <em>set</em> represent themselves.
-For example, <code>[%w_]</code> (or <code>[_%w]</code>)
-represents all alphanumeric characters plus the underscore,
-<code>[0-7]</code> represents the octal digits,
-and <code>[0-7%l%-]</code> represents the octal digits plus
-the lowercase letters plus the '<code>-</code>' character.
-<p>
-The interaction between ranges and classes is not defined.
-Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code>
-have no meaning.
-</li>
-<li><b><code>[^<em>set</em>]</code>:</b>
-represents the complement of <em>set</em>,
-where <em>set</em> is interpreted as above.
-</li>
-</ul><p>
-For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.),
-the corresponding uppercase letter represents the complement of the class.
-For instance, <code>%S</code> represents all non-space characters.
-<p>
-The definitions of letter, space, and other character groups
-depend on the current locale.
-In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>.
-<h4>Pattern Item:</h4><p>
-A <em>pattern item</em> can be
-<ul>
-<li>
-a single character class,
-which matches any single character in the class;
-</li>
-<li>
-a single character class followed by '<code>*</code>',
-which matches 0 or more repetitions of characters in the class.
-These repetition items will always match the longest possible sequence;
-</li>
-<li>
-a single character class followed by '<code>+</code>',
-which matches 1 or more repetitions of characters in the class.
-These repetition items will always match the longest possible sequence;
-</li>
-<li>
-a single character class followed by '<code>-</code>',
-which also matches 0 or more repetitions of characters in the class.
-Unlike '<code>*</code>',
-these repetition items will always match the <em>shortest</em> possible sequence;
-</li>
-<li>
-a single character class followed by '<code>?</code>',
-which matches 0 or 1 occurrence of a character in the class;
-</li>
-<li>
-<code>%<em>n</em></code>, for <em>n</em> between 1 and 9;
-such item matches a substring equal to the <em>n</em>-th captured string
-(see below);
-</li>
-<li>
-<code>%b<em>xy</em></code>, where <em>x</em> and <em>y</em> are two distinct characters;
-such item matches strings that start with&nbsp;<em>x</em>, end with&nbsp;<em>y</em>,
-and where the <em>x</em> and <em>y</em> are <em>balanced</em>.
-This means that, if one reads the string from left to right,
-counting <em>+1</em> for an <em>x</em> and <em>-1</em> for a <em>y</em>,
-the ending <em>y</em> is the first <em>y</em> where the count reaches 0.
-For instance, the item <code>%b()</code> matches expressions with
-balanced parentheses.
-</li>
-</ul>
-<h4>Pattern:</h4><p>
-A <em>pattern</em> is a sequence of pattern items.
-A '<code>^</code>' at the beginning of a pattern anchors the match at the
-beginning of the subject string.
-A '<code>$</code>' at the end of a pattern anchors the match at the
-end of the subject string.
-At other positions,
-'<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves.
-<h4>Captures:</h4><p>
-A pattern can contain sub-patterns enclosed in parentheses;
-they describe <em>captures</em>.
-When a match succeeds, the substrings of the subject string
-that match captures are stored (<em>captured</em>) for future use.
-Captures are numbered according to their left parentheses.
-For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>,
-the part of the string matching <code>"a*(.)%w(%s*)"</code> is
-stored as the first capture (and therefore has number&nbsp;1);
-the character matching "<code>.</code>" is captured with number&nbsp;2,
-and the part matching "<code>%s*</code>" has number&nbsp;3.
-<p>
-As a special case, the empty capture <code>()</code> captures
-the current string position (a number).
-For instance, if we apply the pattern <code>"()aa()"</code> on the
-string <code>"flaaap"</code>, there will be two captures: 3&nbsp;and&nbsp;5.
-<p>
-A pattern cannot contain embedded zeros.  Use <code>%z</code> instead.
-<h2>5.5 - <a name="5.5">Table Manipulation</a></h2><p>
-This library provides generic functions for table manipulation.
-It provides all its functions inside the table <a name="pdf-table"><code>table</code></a>.
-<p>
-Most functions in the table library assume that the table
-represents an array or a list.
-For these functions, when we talk about the "length" of a table
-we mean the result of the length operator.
-<p>
-<hr><h3><a name="pdf-table.concat"><code>table.concat (table [, sep [, i [, j]]])</code></a></h3>
-Given an array where all elements are strings or numbers,
-returns <code>table[i]..sep..table[i+1] &middot;&middot;&middot; sep..table[j]</code>.
-The default value for <code>sep</code> is the empty string,
-the default for <code>i</code> is 1,
-and the default for <code>j</code> is the length of the table.
-If <code>i</code> is greater than <code>j</code>, returns the empty string.
-<p>
-<hr><h3><a name="pdf-table.insert"><code>table.insert (table, [pos,] value)</code></a></h3>
-<p>
-Inserts element <code>value</code> at position <code>pos</code> in <code>table</code>,
-shifting up other elements to open space, if necessary.
-The default value for <code>pos</code> is <code>n+1</code>,
-where <code>n</code> is the length of the table (see <a href="#2.5.5">&sect;2.5.5</a>),
-so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end
-of table <code>t</code>.
-<p>
-<hr><h3><a name="pdf-table.maxn"><code>table.maxn (table)</code></a></h3>
-<p>
-Returns the largest positive numerical index of the given table,
-or zero if the table has no positive numerical indices.
-(To do its job this function does a linear traversal of
-the whole table.) 
-<p>
-<hr><h3><a name="pdf-table.remove"><code>table.remove (table [, pos])</code></a></h3>
-<p>
-Removes from <code>table</code> the element at position <code>pos</code>,
-shifting down other elements to close the space, if necessary.
-Returns the value of the removed element.
-The default value for <code>pos</code> is <code>n</code>,
-where <code>n</code> is the length of the table,
-so that a call <code>table.remove(t)</code> removes the last element
-of table <code>t</code>.
-<p>
-<hr><h3><a name="pdf-table.sort"><code>table.sort (table [, comp])</code></a></h3>
-Sorts table elements in a given order, <em>in-place</em>,
-from <code>table[1]</code> to <code>table[n]</code>,
-where <code>n</code> is the length of the table.
-If <code>comp</code> is given,
-then it must be a function that receives two table elements,
-and returns true
-when the first is less than the second
-(so that <code>not comp(a[i+1],a[i])</code> will be true after the sort).
-If <code>comp</code> is not given,
-then the standard Lua operator <code>&lt;</code> is used instead.
-<p>
-The sort algorithm is not stable;
-that is, elements considered equal by the given order
-may have their relative positions changed by the sort.
-<h2>5.6 - <a name="5.6">Mathematical Functions</a></h2>
-<p>
-This library is an interface to the standard C&nbsp;math library.
-It provides all its functions inside the table <a name="pdf-math"><code>math</code></a>.
-<p>
-<hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3>
-<p>
-Returns the absolute value of <code>x</code>.
-<p>
-<hr><h3><a name="pdf-math.acos"><code>math.acos (x)</code></a></h3>
-<p>
-Returns the arc cosine of <code>x</code> (in radians).
-<p>
-<hr><h3><a name="pdf-math.asin"><code>math.asin (x)</code></a></h3>
-<p>
-Returns the arc sine of <code>x</code> (in radians).
-<p>
-<hr><h3><a name="pdf-math.atan"><code>math.atan (x)</code></a></h3>
-<p>
-Returns the arc tangent of <code>x</code> (in radians).
-<p>
-<hr><h3><a name="pdf-math.atan2"><code>math.atan2 (y, x)</code></a></h3>
-<p>
-Returns the arc tangent of <code>y/x</code> (in radians),
-but uses the signs of both parameters to find the
-quadrant of the result.
-(It also handles correctly the case of <code>x</code> being zero.)
-<p>
-<hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3>
-<p>
-Returns the smallest integer larger than or equal to <code>x</code>.
-<p>
-<hr><h3><a name="pdf-math.cos"><code>math.cos (x)</code></a></h3>
-<p>
-Returns the cosine of <code>x</code> (assumed to be in radians).
-<p>
-<hr><h3><a name="pdf-math.cosh"><code>math.cosh (x)</code></a></h3>
-<p>
-Returns the hyperbolic cosine of <code>x</code>.
-<p>
-<hr><h3><a name="pdf-math.deg"><code>math.deg (x)</code></a></h3>
-<p>
-Returns the angle <code>x</code> (given in radians) in degrees.
-<p>
-<hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3>
-<p>
-Returns the value <em>e<sup>x</sup></em>.
-<p>
-<hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3>
-<p>
-Returns the largest integer smaller than or equal to <code>x</code>.
-<p>
-<hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3>
-<p>
-Returns the remainder of the division of <code>x</code> by <code>y</code>
-that rounds the quotient towards zero.
-<p>
-<hr><h3><a name="pdf-math.frexp"><code>math.frexp (x)</code></a></h3>
-<p>
-Returns <code>m</code> and <code>e</code> such that <em>x = m2<sup>e</sup></em>,
-<code>e</code> is an integer and the absolute value of <code>m</code> is
-in the range <em>[0.5, 1)</em>
-(or zero when <code>x</code> is zero).
-<p>
-<hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3>
-<p>
-The value <code>HUGE_VAL</code>,
-a value larger than or equal to any other numerical value.
-<p>
-<hr><h3><a name="pdf-math.ldexp"><code>math.ldexp (m, e)</code></a></h3>
-<p>
-Returns <em>m2<sup>e</sup></em> (<code>e</code> should be an integer).
-<p>
-<hr><h3><a name="pdf-math.log"><code>math.log (x)</code></a></h3>
-<p>
-Returns the natural logarithm of <code>x</code>.
-<p>
-<hr><h3><a name="pdf-math.log10"><code>math.log10 (x)</code></a></h3>
-<p>
-Returns the base-10 logarithm of <code>x</code>.
-<p>
-<hr><h3><a name="pdf-math.max"><code>math.max (x, &middot;&middot;&middot;)</code></a></h3>
-<p>
-Returns the maximum value among its arguments.
-<p>
-<hr><h3><a name="pdf-math.min"><code>math.min (x, &middot;&middot;&middot;)</code></a></h3>
-<p>
-Returns the minimum value among its arguments.
-<p>
-<hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3>
-<p>
-Returns two numbers,
-the integral part of <code>x</code> and the fractional part of <code>x</code>.
-<p>
-<hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3>
-<p>
-The value of <em>pi</em>.
-<p>
-<hr><h3><a name="pdf-math.pow"><code>math.pow (x, y)</code></a></h3>
-<p>
-Returns <em>x<sup>y</sup></em>.
-(You can also use the expression <code>x^y</code> to compute this value.)
-<p>
-<hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3>
-<p>
-Returns the angle <code>x</code> (given in degrees) in radians.
-<p>
-<hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3>
-<p>
-This function is an interface to the simple
-pseudo-random generator function <code>rand</code> provided by ANSI&nbsp;C.
-(No guarantees can be given for its statistical properties.)
-<p>
-When called without arguments,
-returns a uniform pseudo-random real number
-in the range <em>[0,1)</em>.  
-When called with an integer number <code>m</code>,
-<code>math.random</code> returns
-a uniform pseudo-random integer in the range <em>[1, m]</em>.
-When called with two integer numbers <code>m</code> and <code>n</code>,
-<code>math.random</code> returns a uniform pseudo-random
-integer in the range <em>[m, n]</em>.
-<p>
-<hr><h3><a name="pdf-math.randomseed"><code>math.randomseed (x)</code></a></h3>
-<p>
-Sets <code>x</code> as the "seed"
-for the pseudo-random generator:
-equal seeds produce equal sequences of numbers.
-<p>
-<hr><h3><a name="pdf-math.sin"><code>math.sin (x)</code></a></h3>
-<p>
-Returns the sine of <code>x</code> (assumed to be in radians).
-<p>
-<hr><h3><a name="pdf-math.sinh"><code>math.sinh (x)</code></a></h3>
-<p>
-Returns the hyperbolic sine of <code>x</code>.
-<p>
-<hr><h3><a name="pdf-math.sqrt"><code>math.sqrt (x)</code></a></h3>
-<p>
-Returns the square root of <code>x</code>.
-(You can also use the expression <code>x^0.5</code> to compute this value.)
-<p>
-<hr><h3><a name="pdf-math.tan"><code>math.tan (x)</code></a></h3>
-<p>
-Returns the tangent of <code>x</code> (assumed to be in radians).
-<p>
-<hr><h3><a name="pdf-math.tanh"><code>math.tanh (x)</code></a></h3>
-<p>
-Returns the hyperbolic tangent of <code>x</code>.
-<h2>5.7 - <a name="5.7">Input and Output Facilities</a></h2>
-<p>
-The I/O library provides two different styles for file manipulation.
-The first one uses implicit file descriptors;
-that is, there are operations to set a default input file and a
-default output file,
-and all input/output operations are over these default files.
-The second style uses explicit file descriptors.
-<p>
-When using implicit file descriptors,
-all operations are supplied by table <a name="pdf-io"><code>io</code></a>.
-When using explicit file descriptors,
-the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file descriptor
-and then all operations are supplied as methods of the file descriptor.
-<p>
-The table <code>io</code> also provides
-three predefined file descriptors with their usual meanings from C:
-<a name="pdf-io.stdin"><code>io.stdin</code></a>, <a name="pdf-io.stdout"><code>io.stdout</code></a>, and <a name="pdf-io.stderr"><code>io.stderr</code></a>.
-The I/O library never closes these files.
-<p>
-Unless otherwise stated,
-all I/O functions return <b>nil</b> on failure
-(plus an error message as a second result and
-a system-dependent error code as a third result)
-and some value different from <b>nil</b> on success.
-<p>
-<hr><h3><a name="pdf-io.close"><code>io.close ([file])</code></a></h3>
-<p>
-Equivalent to <code>file:close()</code>.
-Without a <code>file</code>, closes the default output file.
-<p>
-<hr><h3><a name="pdf-io.flush"><code>io.flush ()</code></a></h3>
-<p>
-Equivalent to <code>file:flush</code> over the default output file.
-<p>
-<hr><h3><a name="pdf-io.input"><code>io.input ([file])</code></a></h3>
-<p>
-When called with a file name, it opens the named file (in text mode),
-and sets its handle as the default input file.
-When called with a file handle,
-it simply sets this file handle as the default input file.
-When called without parameters,
-it returns the current default input file.
-<p>
-In case of errors this function raises the error,
-instead of returning an error code.
-<p>
-<hr><h3><a name="pdf-io.lines"><code>io.lines ([filename])</code></a></h3>
-<p>
-Opens the given file name in read mode
-and returns an iterator function that,
-each time it is called,
-returns a new line from the file.
-Therefore, the construction
-<pre>
-     for line in io.lines(filename) do <em>body</em> end
-</pre><p>
-will iterate over all lines of the file.
-When the iterator function detects the end of file,
-it returns <b>nil</b> (to finish the loop) and automatically closes the file.
-<p>
-The call <code>io.lines()</code> (with no file name) is equivalent
-to <code>io.input():lines()</code>;
-that is, it iterates over the lines of the default input file.
-In this case it does not close the file when the loop ends.
-<p>
-<hr><h3><a name="pdf-io.open"><code>io.open (filename [, mode])</code></a></h3>
-<p>
-This function opens a file,
-in the mode specified in the string <code>mode</code>.
-It returns a new file handle,
-or, in case of errors, <b>nil</b> plus an error message.
-<p>
-The <code>mode</code> string can be any of the following:
-<ul>
-<li><b>"r":</b> read mode (the default);</li>
-<li><b>"w":</b> write mode;</li>
-<li><b>"a":</b> append mode;</li>
-<li><b>"r+":</b> update mode, all previous data is preserved;</li>
-<li><b>"w+":</b> update mode, all previous data is erased;</li>
-<li><b>"a+":</b> append update mode, previous data is preserved,
-  writing is only allowed at the end of file.</li>
-</ul><p>
-The <code>mode</code> string can also have a '<code>b</code>' at the end,
-which is needed in some systems to open the file in binary mode.
-This string is exactly what is used in the
-standard&nbsp;C function <code>fopen</code>.
-<p>
-<hr><h3><a name="pdf-io.output"><code>io.output ([file])</code></a></h3>
-<p>
-Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file.
-<p>
-<hr><h3><a name="pdf-io.popen"><code>io.popen (prog [, mode])</code></a></h3>
-<p>
-Starts program <code>prog</code> in a separated process and returns
-a file handle that you can use to read data from this program
-(if <code>mode</code> is <code>"r"</code>, the default)
-or to write data to this program
-(if <code>mode</code> is <code>"w"</code>).
-<p>
-This function is system dependent and is not available
-on all platforms.
-<p>
-<hr><h3><a name="pdf-io.read"><code>io.read (&middot;&middot;&middot;)</code></a></h3>
-<p>
-Equivalent to <code>io.input():read</code>.
-<p>
-<hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3>
-<p>
-Returns a handle for a temporary file.
-This file is opened in update mode
-and it is automatically removed when the program ends.
-<p>
-<hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3>
-<p>
-Checks whether <code>obj</code> is a valid file handle.
-Returns the string <code>"file"</code> if <code>obj</code> is an open file handle,
-<code>"closed file"</code> if <code>obj</code> is a closed file handle,
-or <b>nil</b> if <code>obj</code> is not a file handle.
-<p>
-<hr><h3><a name="pdf-io.write"><code>io.write (&middot;&middot;&middot;)</code></a></h3>
-<p>
-Equivalent to <code>io.output():write</code>.
-<p>
-<hr><h3><a name="pdf-file:close"><code>file:close ()</code></a></h3>
-<p>
-Closes <code>file</code>.
-Note that files are automatically closed when
-their handles are garbage collected,
-but that takes an unpredictable amount of time to happen.
-<p>
-<hr><h3><a name="pdf-file:flush"><code>file:flush ()</code></a></h3>
-<p>
-Saves any written data to <code>file</code>.
-<p>
-<hr><h3><a name="pdf-file:lines"><code>file:lines ()</code></a></h3>
-<p>
-Returns an iterator function that,
-each time it is called,
-returns a new line from the file.
-Therefore, the construction
-<pre>
-     for line in file:lines() do <em>body</em> end
-</pre><p>
-will iterate over all lines of the file.
-(Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file
-when the loop ends.)
-<p>
-<hr><h3><a name="pdf-file:read"><code>file:read (&middot;&middot;&middot;)</code></a></h3>
-<p>
-Reads the file <code>file</code>,
-according to the given formats, which specify what to read.
-For each format,
-the function returns a string (or a number) with the characters read,
-or <b>nil</b> if it cannot read data with the specified format.
-When called without formats,
-it uses a default format that reads the entire next line
-(see below).
-<p>
-The available formats are
-<ul>
-<li><b>"*n":</b>
-reads a number;
-this is the only format that returns a number instead of a string.
-</li>
-<li><b>"*a":</b>
-reads the whole file, starting at the current position.
-On end of file, it returns the empty string.
-</li>
-<li><b>"*l":</b>
-reads the next line (skipping the end of line),
-returning <b>nil</b> on end of file.
-This is the default format.
-</li>
-<li><b><em>number</em>:</b>
-reads a string with up to this number of characters,
-returning <b>nil</b> on end of file.
-If number is zero,
-it reads nothing and returns an empty string,
-or <b>nil</b> on end of file.
-</li>
-</ul>
-<p>
-<hr><h3><a name="pdf-file:seek"><code>file:seek ([whence] [, offset])</code></a></h3>
-<p>
-Sets and gets the file position,
-measured from the beginning of the file,
-to the position given by <code>offset</code> plus a base
-specified by the string <code>whence</code>, as follows:
-<ul>
-<li><b>"set":</b> base is position 0 (beginning of the file);</li>
-<li><b>"cur":</b> base is current position;</li>
-<li><b>"end":</b> base is end of file;</li>
-</ul><p>
-In case of success, function <code>seek</code> returns the final file position,
-measured in bytes from the beginning of the file.
-If this function fails, it returns <b>nil</b>,
-plus a string describing the error.
-<p>
-The default value for <code>whence</code> is <code>"cur"</code>,
-and for <code>offset</code> is 0.
-Therefore, the call <code>file:seek()</code> returns the current
-file position, without changing it;
-the call <code>file:seek("set")</code> sets the position to the
-beginning of the file (and returns 0);
-and the call <code>file:seek("end")</code> sets the position to the
-end of the file, and returns its size.
-<p>
-<hr><h3><a name="pdf-file:setvbuf"><code>file:setvbuf (mode [, size])</code></a></h3>
-<p>
-Sets the buffering mode for an output file.
-There are three available modes:
-<ul>
-<li><b>"no":</b>
-no buffering; the result of any output operation appears immediately.
-</li>
-<li><b>"full":</b>
-full buffering; output operation is performed only
-when the buffer is full (or when you explicitly <code>flush</code> the file
-(see <a href="#pdf-io.flush"><code>io.flush</code></a>)).
-</li>
-<li><b>"line":</b>
-line buffering; output is buffered until a newline is output
-or there is any input from some special files
-(such as a terminal device).
-</li>
-</ul><p>
-For the last two cases, <code>size</code>
-specifies the size of the buffer, in bytes.
-The default is an appropriate size.
-<p>
-<hr><h3><a name="pdf-file:write"><code>file:write (&middot;&middot;&middot;)</code></a></h3>
-<p>
-Writes the value of each of its arguments to
-the <code>file</code>.
-The arguments must be strings or numbers.
-To write other values,
-use <a href="#pdf-tostring"><code>tostring</code></a> or <a href="#pdf-string.format"><code>string.format</code></a> before <code>write</code>.
-<h2>5.8 - <a name="5.8">Operating System Facilities</a></h2>
-<p>
-This library is implemented through table <a name="pdf-os"><code>os</code></a>.
-<p>
-<hr><h3><a name="pdf-os.clock"><code>os.clock ()</code></a></h3>
-<p>
-Returns an approximation of the amount in seconds of CPU time
-used by the program.
-<p>
-<hr><h3><a name="pdf-os.date"><code>os.date ([format [, time]])</code></a></h3>
-<p>
-Returns a string or a table containing date and time,
-formatted according to the given string <code>format</code>.
-<p>
-If the <code>time</code> argument is present,
-this is the time to be formatted
-(see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value).
-Otherwise, <code>date</code> formats the current time.
-<p>
-If <code>format</code> starts with '<code>!</code>',
-then the date is formatted in Coordinated Universal Time.
-After this optional character,
-if <code>format</code> is the string "<code>*t</code>",
-then <code>date</code> returns a table with the following fields:
-<code>year</code> (four digits), <code>month</code> (1--12), <code>day</code> (1--31),
-<code>hour</code> (0--23), <code>min</code> (0--59), <code>sec</code> (0--61),
-<code>wday</code> (weekday, Sunday is&nbsp;1),
-<code>yday</code> (day of the year),
-and <code>isdst</code> (daylight saving flag, a boolean).
-<p>
-If <code>format</code> is not "<code>*t</code>",
-then <code>date</code> returns the date as a string,
-formatted according to the same rules as the C&nbsp;function <code>strftime</code>.
-<p>
-When called without arguments,
-<code>date</code> returns a reasonable date and time representation that depends on
-the host system and on the current locale
-(that is, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>).
-<p>
-<hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3>
-<p>
-Returns the number of seconds from time <code>t1</code> to time <code>t2</code>.
-In POSIX, Windows, and some other systems,
-this value is exactly <code>t2</code><em>-</em><code>t1</code>.
-<p>
-<hr><h3><a name="pdf-os.execute"><code>os.execute ([command])</code></a></h3>
-<p>
-This function is equivalent to the C&nbsp;function <code>system</code>.
-It passes <code>command</code> to be executed by an operating system shell.
-It returns a status code, which is system-dependent.
-If <code>command</code> is absent, then it returns nonzero if a shell is available
-and zero otherwise.
-<p>
-<hr><h3><a name="pdf-os.exit"><code>os.exit ([code])</code></a></h3>
-<p>
-Calls the C&nbsp;function <code>exit</code>,
-with an optional <code>code</code>,
-to terminate the host program.
-The default value for <code>code</code> is the success code.
-<p>
-<hr><h3><a name="pdf-os.getenv"><code>os.getenv (varname)</code></a></h3>
-<p>
-Returns the value of the process environment variable <code>varname</code>,
-or <b>nil</b> if the variable is not defined.
-<p>
-<hr><h3><a name="pdf-os.remove"><code>os.remove (filename)</code></a></h3>
-<p>
-Deletes the file or directory with the given name.
-Directories must be empty to be removed.
-If this function fails, it returns <b>nil</b>,
-plus a string describing the error.
-<p>
-<hr><h3><a name="pdf-os.rename"><code>os.rename (oldname, newname)</code></a></h3>
-<p>
-Renames file or directory named <code>oldname</code> to <code>newname</code>.
-If this function fails, it returns <b>nil</b>,
-plus a string describing the error.
-<p>
-<hr><h3><a name="pdf-os.setlocale"><code>os.setlocale (locale [, category])</code></a></h3>
-<p>
-Sets the current locale of the program.
-<code>locale</code> is a string specifying a locale;
-<code>category</code> is an optional string describing which category to change:
-<code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>,
-<code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>;
-the default category is <code>"all"</code>.
-The function returns the name of the new locale,
-or <b>nil</b> if the request cannot be honored.
-<p>
-If <code>locale</code> is the empty string,
-the current locale is set to an implementation-defined native locale.
-If <code>locale</code> is the string "<code>C</code>",
-the current locale is set to the standard C locale.
-<p>
-When called with <b>nil</b> as the first argument,
-this function only returns the name of the current locale
-for the given category.
-<p>
-<hr><h3><a name="pdf-os.time"><code>os.time ([table])</code></a></h3>
-<p>
-Returns the current time when called without arguments,
-or a time representing the date and time specified by the given table.
-This table must have fields <code>year</code>, <code>month</code>, and <code>day</code>,
-and may have fields <code>hour</code>, <code>min</code>, <code>sec</code>, and <code>isdst</code>
-(for a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function).
-<p>
-The returned value is a number, whose meaning depends on your system.
-In POSIX, Windows, and some other systems, this number counts the number
-of seconds since some given start time (the "epoch").
-In other systems, the meaning is not specified,
-and the number returned by <code>time</code> can be used only as an argument to
-<code>date</code> and <code>difftime</code>.
-<p>
-<hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3>
-<p>
-Returns a string with a file name that can
-be used for a temporary file.
-The file must be explicitly opened before its use
-and explicitly removed when no longer needed.
-<p>
-On some systems (POSIX),
-this function also creates a file with that name,
-to avoid security risks.
-(Someone else might create the file with wrong permissions
-in the time between getting the name and creating the file.)
-You still have to open the file to use it
-and to remove it (even if you do not use it).
-<p>
-When possible,
-you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>,
-which automatically removes the file when the program ends.
-<h2>5.9 - <a name="5.9">The Debug Library</a></h2>
-<p>
-This library provides
-the functionality of the debug interface to Lua programs.
-You should exert care when using this library.
-The functions provided here should be used exclusively for debugging
-and similar tasks, such as profiling.
-Please resist the temptation to use them as a
-usual programming tool:
-they can be very slow.
-Moreover, several of these functions
-violate some assumptions about Lua code
-(e.g., that variables local to a function
-cannot be accessed from outside or
-that userdata metatables cannot be changed by Lua code)
-and therefore can compromise otherwise secure code.
-<p>
-All functions in this library are provided
-inside the <a name="pdf-debug"><code>debug</code></a> table.
-All functions that operate over a thread
-have an optional first argument which is the
-thread to operate over.
-The default is always the current thread.
-<p>
-<hr><h3><a name="pdf-debug.debug"><code>debug.debug ()</code></a></h3>
-<p>
-Enters an interactive mode with the user,
-running each string that the user enters.
-Using simple commands and other debug facilities,
-the user can inspect global and local variables,
-change their values, evaluate expressions, and so on.
-A line containing only the word <code>cont</code> finishes this function,
-so that the caller continues its execution.
-<p>
-Note that commands for <code>debug.debug</code> are not lexically nested
-within any function, and so have no direct access to local variables.
-<p>
-<hr><h3><a name="pdf-debug.getfenv"><code>debug.getfenv (o)</code></a></h3>
-Returns the environment of object <code>o</code>.
-<p>
-<hr><h3><a name="pdf-debug.gethook"><code>debug.gethook ([thread])</code></a></h3>
-<p>
-Returns the current hook settings of the thread, as three values:
-the current hook function, the current hook mask,
-and the current hook count
-(as set by the <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function).
-<p>
-<hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] function [, what])</code></a></h3>
-<p>
-Returns a table with information about a function.
-You can give the function directly,
-or you can give a number as the value of <code>function</code>,
-which means the function running at level <code>function</code> of the call stack
-of the given thread:
-level&nbsp;0 is the current function (<code>getinfo</code> itself);
-level&nbsp;1 is the function that called <code>getinfo</code>;
-and so on.
-If <code>function</code> is a number larger than the number of active functions,
-then <code>getinfo</code> returns <b>nil</b>.
-<p>
-The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>,
-with the string <code>what</code> describing which fields to fill in.
-The default for <code>what</code> is to get all information available,
-except the table of valid lines.
-If present,
-the option '<code>f</code>'
-adds a field named <code>func</code> with the function itself.
-If present,
-the option '<code>L</code>'
-adds a field named <code>activelines</code> with the table of
-valid lines.
-<p>
-For instance, the expression <code>debug.getinfo(1,"n").name</code> returns
-a table with a name for the current function,
-if a reasonable name can be found,
-and the expression <code>debug.getinfo(print)</code>
-returns a table with all available information
-about the <a href="#pdf-print"><code>print</code></a> function.
-<p>
-<hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] level, local)</code></a></h3>
-<p>
-This function returns the name and the value of the local variable
-with index <code>local</code> of the function at level <code>level</code> of the stack.
-(The first parameter or local variable has index&nbsp;1, and so on,
-until the last active local variable.)
-The function returns <b>nil</b> if there is no local
-variable with the given index,
-and raises an error when called with a <code>level</code> out of range.
-(You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.)
-<p>
-Variable names starting with '<code>(</code>' (open parentheses)
-represent internal variables
-(loop control variables, temporaries, and C&nbsp;function locals).
-<p>
-<hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (object)</code></a></h3>
-<p>
-Returns the metatable of the given <code>object</code>
-or <b>nil</b> if it does not have a metatable.
-<p>
-<hr><h3><a name="pdf-debug.getregistry"><code>debug.getregistry ()</code></a></h3>
-<p>
-Returns the registry table (see <a href="#3.5">&sect;3.5</a>).
-<p>
-<hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (func, up)</code></a></h3>
-<p>
-This function returns the name and the value of the upvalue
-with index <code>up</code> of the function <code>func</code>.
-The function returns <b>nil</b> if there is no upvalue with the given index.
-<p>
-<hr><h3><a name="pdf-debug.setfenv"><code>debug.setfenv (object, table)</code></a></h3>
-<p>
-Sets the environment of the given <code>object</code> to the given <code>table</code>.
-Returns <code>object</code>.
-<p>
-<hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3>
-<p>
-Sets the given function as a hook.
-The string <code>mask</code> and the number <code>count</code> describe
-when the hook will be called.
-The string mask may have the following characters,
-with the given meaning:
-<ul>
-<li><b><code>"c"</code>:</b> the hook is called every time Lua calls a function;</li>
-<li><b><code>"r"</code>:</b> the hook is called every time Lua returns from a function;</li>
-<li><b><code>"l"</code>:</b> the hook is called every time Lua enters a new line of code.</li>
-</ul><p>
-With a <code>count</code> different from zero,
-the hook is called after every <code>count</code> instructions.
-<p>
-When called without arguments,
-<a href="#pdf-debug.sethook"><code>debug.sethook</code></a> turns off the hook.
-<p>
-When the hook is called, its first parameter is a string
-describing the event that has triggered its call:
-<code>"call"</code>, <code>"return"</code> (or <code>"tail return"</code>,
-when simulating a return from a tail call),
-<code>"line"</code>, and <code>"count"</code>.
-For line events,
-the hook also gets the new line number as its second parameter.
-Inside a hook,
-you can call <code>getinfo</code> with level&nbsp;2 to get more information about
-the running function
-(level&nbsp;0 is the <code>getinfo</code> function,
-and level&nbsp;1 is the hook function),
-unless the event is <code>"tail return"</code>.
-In this case, Lua is only simulating the return,
-and a call to <code>getinfo</code> will return invalid data.
-<p>
-<hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3>
-<p>
-This function assigns the value <code>value</code> to the local variable
-with index <code>local</code> of the function at level <code>level</code> of the stack.
-The function returns <b>nil</b> if there is no local
-variable with the given index,
-and raises an error when called with a <code>level</code> out of range.
-(You can call <code>getinfo</code> to check whether the level is valid.)
-Otherwise, it returns the name of the local variable.
-<p>
-<hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (object, table)</code></a></h3>
-<p>
-Sets the metatable for the given <code>object</code> to the given <code>table</code>
-(which can be <b>nil</b>).
-<p>
-<hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (func, up, value)</code></a></h3>
-<p>
-This function assigns the value <code>value</code> to the upvalue
-with index <code>up</code> of the function <code>func</code>.
-The function returns <b>nil</b> if there is no upvalue
-with the given index.
-Otherwise, it returns the name of the upvalue.
-<p>
-<hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message] [, level])</code></a></h3>
-<p>
-Returns a string with a traceback of the call stack.
-An optional <code>message</code> string is appended
-at the beginning of the traceback.
-An optional <code>level</code> number tells at which level
-to start the traceback
-(default is 1, the function calling <code>traceback</code>).
-<h1>6 - <a name="6">Lua Stand-alone</a></h1>
-<p>
-Although Lua has been designed as an extension language,
-to be embedded in a host C&nbsp;program,
-it is also frequently used as a stand-alone language.
-An interpreter for Lua as a stand-alone language,
-called simply <code>lua</code>,
-is provided with the standard distribution.
-The stand-alone interpreter includes
-all standard libraries, including the debug library.
-Its usage is:
-<pre>
-     lua [options] [script [args]]
-</pre><p>
-The options are:
-<ul>
-<li><b><code>-e <em>stat</em></code>:</b> executes string <em>stat</em>;</li>
-<li><b><code>-l <em>mod</em></code>:</b> "requires" <em>mod</em>;</li>
-<li><b><code>-i</code>:</b> enters interactive mode after running <em>script</em>;</li>
-<li><b><code>-v</code>:</b> prints version information;</li>
-<li><b><code>--</code>:</b> stops handling options;</li>
-<li><b><code>-</code>:</b> executes <code>stdin</code> as a file and stops handling options.</li>
-</ul><p>
-After handling its options, <code>lua</code> runs the given <em>script</em>,
-passing to it the given <em>args</em> as string arguments.
-When called without arguments,
-<code>lua</code> behaves as <code>lua -v -i</code>
-when the standard input (<code>stdin</code>) is a terminal,
-and as <code>lua -</code> otherwise.
-<p>
-Before running any argument,
-the interpreter checks for an environment variable <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a>.
-If its format is <code>@<em>filename</em></code>,
-then <code>lua</code> executes the file.
-Otherwise, <code>lua</code> executes the string itself.
-<p>
-All options are handled in order, except <code>-i</code>.
-For instance, an invocation like
-<pre>
-     $ lua -e'a=1' -e 'print(a)' script.lua
-</pre><p>
-will first set <code>a</code> to 1, then print the value of <code>a</code> (which is '<code>1</code>'),
-and finally run the file <code>script.lua</code> with no arguments.
-(Here <code>$</code> is the shell prompt. Your prompt may be different.)
-<p>
-Before starting to run the script,
-<code>lua</code> collects all arguments in the command line
-in a global table called <code>arg</code>.
-The script name is stored at index 0,
-the first argument after the script name goes to index 1,
-and so on.
-Any arguments before the script name
-(that is, the interpreter name plus the options)
-go to negative indices.
-For instance, in the call
-<pre>
-     $ lua -la b.lua t1 t2
-</pre><p>
-the interpreter first runs the file <code>a.lua</code>,
-then creates a table
-<pre>
-     arg = { [-2] = "lua", [-1] = "-la",
-             [0] = "b.lua",
-             [1] = "t1", [2] = "t2" }
-</pre><p>
-and finally runs the file <code>b.lua</code>.
-The script is called with <code>arg[1]</code>, <code>arg[2]</code>, &middot;&middot;&middot;
-as arguments;
-it can also access these arguments with the vararg expression '<code>...</code>'.
-<p>
-In interactive mode,
-if you write an incomplete statement,
-the interpreter waits for its completion
-by issuing a different prompt.
-<p>
-If the global variable <a name="pdf-_PROMPT"><code>_PROMPT</code></a> contains a string,
-then its value is used as the prompt.
-Similarly, if the global variable <a name="pdf-_PROMPT2"><code>_PROMPT2</code></a> contains a string,
-its value is used as the secondary prompt
-(issued during incomplete statements).
-Therefore, both prompts can be changed directly on the command line
-or in any Lua programs by assigning to <code>_PROMPT</code>.
-See the next example:
-<pre>
-     $ lua -e"_PROMPT='myprompt&gt; '" -i
-</pre><p>
-(The outer pair of quotes is for the shell,
-the inner pair is for Lua.)
-Note the use of <code>-i</code> to enter interactive mode;
-otherwise,
-the program would just end silently
-right after the assignment to <code>_PROMPT</code>.
-<p>
-To allow the use of Lua as a
-script interpreter in Unix systems,
-the stand-alone interpreter skips
-the first line of a chunk if it starts with <code>#</code>.
-Therefore, Lua scripts can be made into executable programs
-by using <code>chmod +x</code> and the&nbsp;<code>#!</code> form,
-as in
-<pre>
-     #!/usr/local/bin/lua
-</pre><p>
-(Of course,
-the location of the Lua interpreter may be different in your machine.
-If <code>lua</code> is in your <code>PATH</code>,
-then 
-<pre>
-     #!/usr/bin/env lua
-</pre><p>
-is a more portable solution.) 
-<h1>7 - <a name="7">Incompatibilities with the Previous Version</a></h1>
-<p>
-Here we list the incompatibilities that you may find when moving a program
-from Lua&nbsp;5.0 to Lua&nbsp;5.1.
-You can avoid most of the incompatibilities compiling Lua with
-appropriate options (see file <code>luaconf.h</code>).
-However,
-all these compatibility options will be removed in the next version of Lua.
-<h2>7.1 - <a name="7.1">Changes in the Language</a></h2>
-<ul>
-<li>
-The vararg system changed from the pseudo-argument <code>arg</code> with a
-table with the extra arguments to the vararg expression.
-(See compile-time option <code>LUA_COMPAT_VARARG</code> in <code>luaconf.h</code>.)
-</li>
-<li>
-There was a subtle change in the scope of the implicit
-variables of the <b>for</b> statement and for the <b>repeat</b> statement.
-</li>
-<li>
-The long string/long comment syntax (<code>[[<em>string</em>]]</code>)
-does not allow nesting.
-You can use the new syntax (<code>[=[<em>string</em>]=]</code>) in these cases.
-(See compile-time option <code>LUA_COMPAT_LSTR</code> in <code>luaconf.h</code>.)
-</li>
-</ul>
-<h2>7.2 - <a name="7.2">Changes in the Libraries</a></h2>
-<ul>
-<li>
-Function <code>string.gfind</code> was renamed <a href="#pdf-string.gmatch"><code>string.gmatch</code></a>.
-(See compile-time option <code>LUA_COMPAT_GFIND</code> in <code>luaconf.h</code>.)
-</li>
-<li>
-When <a href="#pdf-string.gsub"><code>string.gsub</code></a> is called with a function as its
-third argument,
-whenever this function returns <b>nil</b> or <b>false</b> the
-replacement string is the whole match,
-instead of the empty string.
-</li>
-<li>
-Function <code>table.setn</code> was deprecated.
-Function <code>table.getn</code> corresponds
-to the new length operator (<code>#</code>);
-use the operator instead of the function.
-(See compile-time option <code>LUA_COMPAT_GETN</code> in <code>luaconf.h</code>.)
-</li>
-<li>
-Function <code>loadlib</code> was renamed <a href="#pdf-package.loadlib"><code>package.loadlib</code></a>.
-(See compile-time option <code>LUA_COMPAT_LOADLIB</code> in <code>luaconf.h</code>.)
-</li>
-<li>
-Function <code>math.mod</code> was renamed <a href="#pdf-math.fmod"><code>math.fmod</code></a>.
-(See compile-time option <code>LUA_COMPAT_MOD</code> in <code>luaconf.h</code>.)
-</li>
-<li>
-Functions <code>table.foreach</code> and <code>table.foreachi</code> are deprecated.
-You can use a for loop with <code>pairs</code> or <code>ipairs</code> instead.
-</li>
-<li>
-There were substantial changes in function <a href="#pdf-require"><code>require</code></a> due to
-the new module system.
-However, the new behavior is mostly compatible with the old,
-but <code>require</code> gets the path from <a href="#pdf-package.path"><code>package.path</code></a> instead
-of from <code>LUA_PATH</code>.
-</li>
-<li>
-Function <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> has different arguments.
-Function <code>gcinfo</code> is deprecated;
-use <code>collectgarbage("count")</code> instead.
-</li>
-</ul>
-<h2>7.3 - <a name="7.3">Changes in the API</a></h2>
-<ul>
-<li>
-The <code>luaopen_*</code> functions (to open libraries)
-cannot be called directly,
-like a regular C function.
-They must be called through Lua,
-like a Lua function.
-</li>
-<li>
-Function <code>lua_open</code> was replaced by <a href="#lua_newstate"><code>lua_newstate</code></a> to
-allow the user to set a memory-allocation function.
-You can use <a href="#luaL_newstate"><code>luaL_newstate</code></a> from the standard library to
-create a state with a standard allocation function
-(based on <code>realloc</code>).
-</li>
-<li>
-Functions <code>luaL_getn</code> and <code>luaL_setn</code>
-(from the auxiliary library) are deprecated.
-Use <a href="#lua_objlen"><code>lua_objlen</code></a> instead of <code>luaL_getn</code>
-and nothing instead of <code>luaL_setn</code>.
-</li>
-<li>
-Function <code>luaL_openlib</code> was replaced by <a href="#luaL_register"><code>luaL_register</code></a>.
-</li>
-<li>
-Function <code>luaL_checkudata</code> now throws an error when the given value
-is not a userdata of the expected type.
-(In Lua&nbsp;5.0 it returned <code>NULL</code>.)
-</li>
-</ul>
-<h1>8 - <a name="8">The Complete Syntax of Lua</a></h1>
-<p>
-Here is the complete syntax of Lua in extended BNF.
-(It does not describe operator precedences.)
-<pre>
-        chunk ::= {stat [`<b>;</b>&acute;]} [laststat [`<b>;</b>&acute;]]
-        block ::= chunk
-        stat ::=  varlist `<b>=</b>&acute; explist | 
-                 functioncall | 
-                 <b>do</b> block <b>end</b> | 
-                 <b>while</b> exp <b>do</b> block <b>end</b> | 
-                 <b>repeat</b> block <b>until</b> exp | 
-                 <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> | 
-                 <b>for</b> Name `<b>=</b>&acute; exp `<b>,</b>&acute; exp [`<b>,</b>&acute; exp] <b>do</b> block <b>end</b> | 
-                 <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> | 
-                 <b>function</b> funcname funcbody | 
-                 <b>local</b> <b>function</b> Name funcbody | 
-                 <b>local</b> namelist [`<b>=</b>&acute; explist] 
-        laststat ::= <b>return</b> [explist] | <b>break</b>
-        funcname ::= Name {`<b>.</b>&acute; Name} [`<b>:</b>&acute; Name]
-        varlist ::= var {`<b>,</b>&acute; var}
-        var ::=  Name | prefixexp `<b>[</b>&acute; exp `<b>]</b>&acute; | prefixexp `<b>.</b>&acute; Name 
-        namelist ::= Name {`<b>,</b>&acute; Name}
-        explist ::= {exp `<b>,</b>&acute;} exp
-        exp ::=  <b>nil</b> | <b>false</b> | <b>true</b> | Number | String | `<b>...</b>&acute; | function | 
-                 prefixexp | tableconstructor | exp binop exp | unop exp 
-        prefixexp ::= var | functioncall | `<b>(</b>&acute; exp `<b>)</b>&acute;
-        functioncall ::=  prefixexp args | prefixexp `<b>:</b>&acute; Name args 
-        args ::=  `<b>(</b>&acute; [explist] `<b>)</b>&acute; | tableconstructor | String 
-        function ::= <b>function</b> funcbody
-        funcbody ::= `<b>(</b>&acute; [parlist] `<b>)</b>&acute; block <b>end</b>
-        parlist ::= namelist [`<b>,</b>&acute; `<b>...</b>&acute;] | `<b>...</b>&acute;
-        tableconstructor ::= `<b>{</b>&acute; [fieldlist] `<b>}</b>&acute;
-        fieldlist ::= field {fieldsep field} [fieldsep]
-        field ::= `<b>[</b>&acute; exp `<b>]</b>&acute; `<b>=</b>&acute; exp | Name `<b>=</b>&acute; exp | exp
-        fieldsep ::= `<b>,</b>&acute; | `<b>;</b>&acute;
-        binop ::= `<b>+</b>&acute; | `<b>-</b>&acute; | `<b>*</b>&acute; | `<b>/</b>&acute; | `<b>^</b>&acute; | `<b>%</b>&acute; | `<b>..</b>&acute; | 
-                 `<b>&lt;</b>&acute; | `<b>&lt;=</b>&acute; | `<b>&gt;</b>&acute; | `<b>&gt;=</b>&acute; | `<b>==</b>&acute; | `<b>~=</b>&acute; | 
-                 <b>and</b> | <b>or</b>
-        unop ::= `<b>-</b>&acute; | <b>not</b> | `<b>#</b>&acute;
-</pre>
-<p>
-<HR>
-<SMALL>
-Last update:
-Mon Aug 18 13:25:46 BRT 2008
-</SMALL>
-<!--
-Last change: revised for Lua 5.1.4
-->
-</body></html>