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<h2><a name="introduction"></a>Introduction</h2>

<p>LuaExpat is a <a href="http://www.saxproject.org/">SAX</a> XML
parser based on the <a href="http://www.libexpat.org/">Expat</a> library.
SAX is the <em>Simple API for XML</em> and allows programs to:
</p>

<ul>
    <li>process a XML document incrementally, thus being able to handle
    huge documents without memory penalties;</li>
    
    <li>register handler functions which are called by the parser during
    the processing of the document, handling the document elements or
    text.</li>
</ul>

<p>With an event-based API like SAX the XML document can be fed to
the parser in chunks, and the parsing begins as soon as the parser
receives the first document chunk. LuaExpat reports parsing events
(such as the start and end of elements) directly to the application
through callbacks. The parsing of huge documents can benefit from
this piecemeal operation.</p>

<p>LuaExpat is distributed as a library and a file <code>lom.lua</code> that
implements the <a href="lom.html">Lua Object Model</a>.</p>


<h2><a name="building"></a>Building</h2>

<p>
LuaExpat could be built to Lua 5.1 or to Lua 5.2.
In both cases,
the language library and headers files for the desired version
must be installed properly.
LuaExpat also depends on Expat 2.0.0+ which should also be installed.
</p>
<p>
LuaExpat offers a Makefile and a separate configuration file,
<code>config</code>,
which should be edited to suit the particularities of the target platform
before running
<code>make</code>.
The file has some definitions like paths to the external libraries,
compiler options and the like.
One important definition is the version of Lua language,
which is not obtained from the installed software.
</p>


<h2><a name="installation"></a>Installation</h2>

<p>The compiled binary file should be copied to a directory in your
<a href="http://www.lua.org/manual/5.1/manual.html#pdf-package.cpath">C path</a>.
Lua 5.0 users should also install
<a href="http://www.keplerproject.org/compat">Compat-5.1</a>.</p>

<p>Windows users can use the binary version of LuaExpat (<code>lxp.dll</code>, compatible with
<a href="http://luabinaries.luaforge.net">LuaBinaries</a>) available at
<a href="http://luaforge.net/projects/luaexpat/files">LuaForge</a>.</p>

<p>The file <code>lom.lua</code> should be copied to a directory in your
<a href="http://www.lua.org/manual/5.1/manual.html#pdf-package.path">Lua path</a>.</p>

<h2><a name="parser"></a>Parser objects</h2>

<p>Usually SAX implementations base all operations on the
concept of a parser that allows the registration of callback
functions. LuaExpat offers the same functionality but uses a
different registration method, based on a table of callbacks. This
table contains references to the callback functions which are
responsible for the handling of the document parts. The parser will
assume no behaviour for any undeclared callbacks.</p>

<h4>Constructor</h4>

<dl class="reference">
    <dt><strong>lxp.new(<em>callbacks [, separator[, merge_character_data]]</em>)</strong></dt>
    <dd>The parser is created by a call to the function <strong>lxp.new</strong>,
    which returns the created parser or raises a Lua error. It
    receives the callbacks table and optionally the parser <a href="#separator">
    separator character</a> used in the namespace expanded element names.
    If <em>merge_character_data</em> is false then LuaExpat will not combine multiple
    CharacterData calls into one. For more info on this behaviour see CharacterData below.</dd>
</dl>

<h4>Methods</h4>

<dl class="reference">
    <dt><strong>parser:close()</strong></dt>
    <dd>Closes the parser, freeing all memory used by it. A call to
    parser:close() without a previous call to parser:parse() could
    result in an error.</dd>
   
    <dt><strong>parser:getbase()</strong></dt>
    <dd>Returns the base for resolving relative URIs.</dd>
    
    <dt><strong>parser:getcallbacks()</strong></dt>
    <dd>Returns the callbacks table.</dd>
    
    <dt><strong>parser:parse(s)</strong></dt>
    <dd>Parse some more of the document. The string <em>s</em> contains
    part (or perhaps all) of the document. When called without
    arguments the document is closed (but the parser still has to be
    closed).<br/>
    The function returns a non nil value when the parser has been
    succesfull, and when the parser finds an error it returns five
    results: nil, <em>msg</em>, <em>line</em>, <em>col</em>, and
    <em>pos</em>, which are the error message, the line number,
    column number and absolute position of the error in the XML document.</dd>

    <dt><strong>parser:pos()</strong></dt>
    <dd>Returns three results: the current parsing line, column, and
    absolute position.</dd>

    <dt><strong>parser:getcurrentbytecount()</strong></dt>
    <dd>Return the number of bytes of input corresponding to the current
    event. This function can only be called inside a handler, in other
    contexts it will return 0. Do not use inside a CharacterData handler
    unless CharacterData merging has been disabled (see lxp.new).</dd>

    <dt><strong>parser:setbase(base)</strong></dt>
    <dd>Sets the <em>base</em> to be used for resolving relative URIs in
    system identifiers.</dd>

    <dt><strong>parser:setencoding(encoding)</strong></dt>
    <dd>Set the encoding to be used by the parser. There are four
    built-in encodings, passed as strings: "US-ASCII",
    "UTF-8", "UTF-16", and "ISO-8859-1".</dd>

    <dt><strong>parser:stop()</strong></dt>
    <dd>Abort the parser and prevent it from parsing any further
    through the data it was last passed. Use to halt parsing the
    document when an error is discovered inside a callback, for
    example. The parser object cannot accept more data after
    this call.</dd>
</dl>

<h4>Callbacks</h4>

<p>The Lua callbacks define the handlers of the parser events. The
use of a table in the parser constructor has some advantages over
the registration of callbacks, since there is no need for for the API
to provide a way to manipulate callbacks.</p>

<p>Another difference lies in the behaviour of the callbacks during
the parsing itself. The callback table contains references to the
functions that can be redefined at will. The only restriction is
that only the callbacks present in the table at creation time
will be called.</p>

<p>The callbacks table indices are named after the equivalent Expat
callbacks:<br />
<em>CharacterData</em>, <em>Comment</em>,
<em>Default</em>, <em>DefaultExpand</em>, <em>EndCDataSection</em>,
<em>EndElement</em>, <em>EndNamespaceDecl</em>,
<em>ExternalEntityRef</em>, <em>NotStandalone</em>,
<em>NotationDecl</em>, <em>ProcessingInstruction</em>,
<em>StartCDataSection</em>, <em>StartElement</em>,
<em>StartNamespaceDecl</em>, <em>UnparsedEntityDecl</em>,
<em>XmlDecl</em> and <em>StartDoctypeDecl</em>.</p>

<p>These indices can be references to functions with
specific signatures, as seen below. The parser constructor also
checks the presence of a field called <em>_nonstrict</em> in the
callbacks table. If <em>_nonstrict</em> is absent, only valid
callback names are accepted as indices in the table
(Defaultexpanded would be considered an error for example). If
<em>_nonstrict</em> is defined, any other fieldnames can be
used (even if not called at all).</p>

<p>The callbacks can optionally be defined as <code>false</code>,
acting thus as placeholders for future assignment of functions.</p>

<p>Every callback function receives as the first parameter the
calling parser itself, thus allowing the same functions to be used
for more than one parser for example.</p>

<dl class="reference">
    <dt><strong>callbacks.CharacterData = function(parser, string)</strong></dt>
    <dd>Called when the <em>parser</em> recognizes an XML CDATA <em>string</em>.
    Note that LuaExpat automatically combines multiple CharacterData events
    from Expat into a single call to this handler, unless <em>merge_character_data</em>
    is set to false when calling lxp.new().</dd>

    <dt><strong>callbacks.Comment = function(parser, string)</strong></dt>
    <dd>Called when the <em>parser</em> recognizes an XML comment
    <em>string</em>.</dd>
    
    <dt><strong>callbacks.Default = function(parser, string)</strong></dt>
    <dd>Called when the <em>parser</em> has a <em>string</em>
    corresponding to any characters in the document which wouldn't
    otherwise be handled. Using this handler has the side effect of
    turning off expansion of references to internally defined general
    entities. Instead these references are passed to the default
    handler.</dd>

    <dt><strong>callbacks.DefaultExpand = function(parser, string)</strong></dt>
    <dd>Called when the <em>parser</em> has a <em>string</em>
    corresponding to any characters in the document which wouldn't
    otherwise be handled. Using this handler doesn't affect expansion
    of internal entity references.</dd>

    <dt><strong>callbacks.EndCdataSection = function(parser)</strong></dt>
    <dd>Called when the <em>parser</em> detects the end of a CDATA
    section.</dd>

    <dt><strong>callbacks.EndElement = function(parser, elementName)</strong></dt>
    <dd>Called when the <em>parser</em> detects the ending of an XML
    element with <em>elementName</em>.</dd>

    <dt><strong>callbacks.EndNamespaceDecl = function(parser, namespaceName)</strong></dt>
    <dd>Called when the <em>parser</em> detects the ending of an XML
    namespace with <em>namespaceName</em>. The handling of the end
    namespace is done after the handling of the end tag for the element
    the namespace is associated with.</dd>

    <dt><strong>callbacks.ExternalEntityRef = function(parser, subparser, base, systemId, publicId)</strong></dt>
    <dd>Called when the <em>parser</em> detects an external entity
    reference.<br/><br/>
    The <em>subparser</em> is a LuaExpat parser created with the
    same callbacks and Expat context as the <em>parser</em> and should
    be used to parse the external entity.<br/>
    The <em>base</em> parameter is the base to use for relative
    system identifiers. It is set by parser:setbase and may be nil.<br/>
    The <em>systemId</em> parameter is the system identifier
    specified in the entity declaration and is never nil.<br/>
    The <em>publicId</em> parameter is the public id given in the
    entity declaration and may be nil.</dd>

    <dt><strong>callbacks.NotStandalone = function(parser)</strong></dt>
    <dd>Called when the <em>parser</em> detects that the document is not
    "standalone". This happens when there is an external subset or a
    reference to a parameter entity, but the document does not have standalone set
    to "yes" in an XML declaration.</dd>

    <dt><strong>callbacks.NotationDecl = function(parser, notationName, base, systemId, publicId)</strong></dt>
    <dd>Called when the <em>parser</em> detects XML notation
    declarations with <em>notationName</em><br/>
    The <em>base</em> parameter is the base to use for relative
    system identifiers. It is set by parser:setbase and may be nil.<br/>
    The <em>systemId</em> parameter is the system identifier
    specified in the entity declaration and is never nil.<br/>
    The <em>publicId</em> parameter is the public id given in the
    entity declaration and may be nil.</dd>

    <dt><strong>callbacks.ProcessingInstruction = function(parser, target, data)</strong></dt>
    <dd>Called when the <em>parser</em> detects XML processing
    instructions. The <em>target</em> is the first word in the
    processing instruction. The <em>data</em> is the rest of the
    characters in it after skipping all whitespace after the initial
    word.</dd>

    <dt><strong>callbacks.StartCdataSection = function(parser)</strong></dt>
    <dd>Called when the <em>parser</em> detects the begining of an XML
    CDATA section.</dd>
    
    <dt><strong>callbacks.XmlDecl = function(parser, version, encoding)</strong></dt>
    <dd>Called when the <em>parser</em> encounters an XML document declaration (these are
    optional, and valid only at the start of the document). The callback receives
    the declared XML <em>version</em> and document <em>encoding</em>.</dd>
    
    <dt><strong>callbacks.StartElement = function(parser, elementName, attributes)</strong></dt>
    <dd>Called when the <em>parser</em> detects the begining of an XML
    element with <em>elementName</em>.<br/>
    The <em>attributes</em> parameter is a Lua table with all the
    element attribute names and values. The table contains an entry for
    every attribute in the element start tag and entries for the
    default attributes for that element.<br/>
    The attributes are listed by name (including the inherited ones)
    and by position (inherited attributes are not considered in the
    position list).<br/>
    As an example if the <em>book</em> element has attributes
    <em>author</em>, <em>title</em> and an optional <em>format</em>
    attribute (with "printed" as default value),
<pre class="example">
&lt;book author="Ierusalimschy, Roberto" title="Programming in Lua"&gt;
</pre>
    would be represented as<br/> 
<pre class="example">
{[1] = "Ierusalimschy, Roberto",
 [2] = "Programming in Lua",
 author = "Ierusalimschy, Roberto",
 format = "printed",
 title = "Programming in Lua"}
</pre></dd>

    <dt><strong>callbacks.StartNamespaceDecl = function(parser, namespaceName)</strong></dt>
    <dd>Called when the <em>parser</em> detects an XML namespace
    declaration with <em>namespaceName</em>. Namespace declarations
    occur inside start tags, but the StartNamespaceDecl handler is
    called before the StartElement handler for each namespace declared
    in that start tag.</dd>

    <dt><strong>callbacks.UnparsedEntityDecl = function(parser, entityName, base, systemId, publicId, notationName)</strong></dt>
    <dd>Called when the <em>parser</em> receives declarations of
    unparsed entities. These are entity declarations that have a
    notation (NDATA) field.<br/>
    As an example, in the chunk
<pre class="example">
&lt;!ENTITY logo SYSTEM "images/logo.gif" NDATA gif&gt;
</pre>
    <em>entityName</em> would be "logo", <em>systemId</em> would be
    "images/logo.gif" and <em>notationName</em> would be "gif".
    For this example the <em>publicId</em> parameter would be nil.
    The <em>base</em> parameter would be whatever has been set with
    <code>parser:setbase</code>. If not set, it would be nil.</dd>

    <dt><strong>callbacks.StartDoctypeDecl = function(parser, name, sysid, pubid, has_internal_subset)</strong></dt>
    <dd>Called when the <em>parser</em> detects the beginning of an XML
    DTD (DOCTYPE) section. These precede the XML root element and take
    the form:
<pre class="example">
&lt;!DOCTYPE root_elem PUBLIC "example"&gt;
</pre>
    </dd>
</dl>

<h4><a name="separator"></a>The separator character</h4>

<p>The optional separator character in the parser constructor
defines the character used in the namespace expanded element names.
The separator character is optional (if not defined the parser will
not handle namespaces) but if defined it must be different from
the character '\0'.</p>

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