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<title>13.10.1 ContentHandler Objects </title>
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<H2><A NAME="SECTION00151010000000000000000"></A><A NAME="content-handler-objects"></A>
<BR>
13.10.1 ContentHandler Objects
</H2>
<P>
Users are expected to subclass <tt class="class">ContentHandler</tt> to support their
application. The following methods are called by the parser on the
appropriate events in the input document:
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4489' xml:id='l2h-4489' class="method">setDocumentLocator</tt></b>(</nobr></td>
<td><var>locator</var>)</td></tr></table></dt>
<dd>
Called by the parser to give the application a locator for locating
the origin of document events.
<P>
SAX parsers are strongly encouraged (though not absolutely required)
to supply a locator: if it does so, it must supply the locator to
the application by invoking this method before invoking any of the
other methods in the DocumentHandler interface.
<P>
The locator allows the application to determine the end position of
any document-related event, even if the parser is not reporting an
error. Typically, the application will use this information for
reporting its own errors (such as character content that does not
match an application's business rules). The information returned by
the locator is probably not sufficient for use with a search engine.
<P>
Note that the locator will return correct information only during
the invocation of the events in this interface. The application
should not attempt to use it at any other time.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4490' xml:id='l2h-4490' class="method">startDocument</tt></b>(</nobr></td>
<td><var></var>)</td></tr></table></dt>
<dd>
Receive notification of the beginning of a document.
<P>
The SAX parser will invoke this method only once, before any other
methods in this interface or in DTDHandler (except for
<tt class="method">setDocumentLocator()</tt>).
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4491' xml:id='l2h-4491' class="method">endDocument</tt></b>(</nobr></td>
<td><var></var>)</td></tr></table></dt>
<dd>
Receive notification of the end of a document.
<P>
The SAX parser will invoke this method only once, and it will be the
last method invoked during the parse. The parser shall not invoke
this method until it has either abandoned parsing (because of an
unrecoverable error) or reached the end of input.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4492' xml:id='l2h-4492' class="method">startPrefixMapping</tt></b>(</nobr></td>
<td><var>prefix, uri</var>)</td></tr></table></dt>
<dd>
Begin the scope of a prefix-URI Namespace mapping.
<P>
The information from this event is not necessary for normal
Namespace processing: the SAX XML reader will automatically replace
prefixes for element and attribute names when the
<code>feature_namespaces</code> feature is enabled (the default).
<P>
There are cases, however, when applications need to use prefixes in
character data or in attribute values, where they cannot safely be
expanded automatically; the <tt class="method">startPrefixMapping()</tt> and
<tt class="method">endPrefixMapping()</tt> events supply the information to the
application to expand prefixes in those contexts itself, if
necessary.
<P>
Note that <tt class="method">startPrefixMapping()</tt> and
<tt class="method">endPrefixMapping()</tt> events are not guaranteed to be properly
nested relative to each-other: all <tt class="method">startPrefixMapping()</tt>
events will occur before the corresponding <tt class="method">startElement()</tt>
event, and all <tt class="method">endPrefixMapping()</tt> events will occur after
the corresponding <tt class="method">endElement()</tt> event, but their order is
not guaranteed.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4493' xml:id='l2h-4493' class="method">endPrefixMapping</tt></b>(</nobr></td>
<td><var>prefix</var>)</td></tr></table></dt>
<dd>
End the scope of a prefix-URI mapping.
<P>
See <tt class="method">startPrefixMapping()</tt> for details. This event will
always occur after the corresponding <tt class="method">endElement()</tt> event,
but the order of <tt class="method">endPrefixMapping()</tt> events is not otherwise
guaranteed.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4494' xml:id='l2h-4494' class="method">startElement</tt></b>(</nobr></td>
<td><var>name, attrs</var>)</td></tr></table></dt>
<dd>
Signals the start of an element in non-namespace mode.
<P>
The <var>name</var> parameter contains the raw XML 1.0 name of the
element type as a string and the <var>attrs</var> parameter holds an
object of the <a class="ulink" href="attributes-objects.html"
><tt class="class">Attributes</tt>
interface</a> containing the attributes of the
element. The object passed as <var>attrs</var> may be re-used by the
parser; holding on to a reference to it is not a reliable way to
keep a copy of the attributes. To keep a copy of the attributes,
use the <tt class="method">copy()</tt> method of the <var>attrs</var> object.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4495' xml:id='l2h-4495' class="method">endElement</tt></b>(</nobr></td>
<td><var>name</var>)</td></tr></table></dt>
<dd>
Signals the end of an element in non-namespace mode.
<P>
The <var>name</var> parameter contains the name of the element type, just
as with the <tt class="method">startElement()</tt> event.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4496' xml:id='l2h-4496' class="method">startElementNS</tt></b>(</nobr></td>
<td><var>name, qname, attrs</var>)</td></tr></table></dt>
<dd>
Signals the start of an element in namespace mode.
<P>
The <var>name</var> parameter contains the name of the element type as a
<code>(<var>uri</var>, <var>localname</var>)</code> tuple, the <var>qname</var> parameter
contains the raw XML 1.0 name used in the source document, and the
<var>attrs</var> parameter holds an instance of the
<a class="ulink" href="attributes-ns-objects.html"
><tt class="class">AttributesNS</tt> interface</a>
containing the attributes of the element. If no namespace is
associated with the element, the <var>uri</var> component of <var>name</var>
will be <code>None</code>. The object passed as <var>attrs</var> may be
re-used by the parser; holding on to a reference to it is not a
reliable way to keep a copy of the attributes. To keep a copy of
the attributes, use the <tt class="method">copy()</tt> method of the <var>attrs</var>
object.
<P>
Parsers may set the <var>qname</var> parameter to <code>None</code>, unless the
<code>feature_namespace_prefixes</code> feature is activated.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4497' xml:id='l2h-4497' class="method">endElementNS</tt></b>(</nobr></td>
<td><var>name, qname</var>)</td></tr></table></dt>
<dd>
Signals the end of an element in namespace mode.
<P>
The <var>name</var> parameter contains the name of the element type, just
as with the <tt class="method">startElementNS()</tt> method, likewise the
<var>qname</var> parameter.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4498' xml:id='l2h-4498' class="method">characters</tt></b>(</nobr></td>
<td><var>content</var>)</td></tr></table></dt>
<dd>
Receive notification of character data.
<P>
The Parser will call this method to report each chunk of character
data. SAX parsers may return all contiguous character data in a
single chunk, or they may split it into several chunks; however, all
of the characters in any single event must come from the same
external entity so that the Locator provides useful information.
<P>
<var>content</var> may be a Unicode string or a byte string; the
<code>expat</code> reader module produces always Unicode strings.
<P>
<span class="note"><b class="label">Note:</b>
The earlier SAX 1 interface provided by the Python
XML Special Interest Group used a more Java-like interface for this
method. Since most parsers used from Python did not take advantage
of the older interface, the simpler signature was chosen to replace
it. To convert old code to the new interface, use <var>content</var>
instead of slicing content with the old <var>offset</var> and
<var>length</var> parameters.</span>
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4499' xml:id='l2h-4499' class="method">ignorableWhitespace</tt></b>(</nobr></td>
<td><var>whitespace</var>)</td></tr></table></dt>
<dd>
Receive notification of ignorable whitespace in element content.
<P>
Validating Parsers must use this method to report each chunk
of ignorable whitespace (see the W3C XML 1.0 recommendation,
section 2.10): non-validating parsers may also use this method
if they are capable of parsing and using content models.
<P>
SAX parsers may return all contiguous whitespace in a single
chunk, or they may split it into several chunks; however, all
of the characters in any single event must come from the same
external entity, so that the Locator provides useful
information.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4500' xml:id='l2h-4500' class="method">processingInstruction</tt></b>(</nobr></td>
<td><var>target, data</var>)</td></tr></table></dt>
<dd>
Receive notification of a processing instruction.
<P>
The Parser will invoke this method once for each processing
instruction found: note that processing instructions may occur
before or after the main document element.
<P>
A SAX parser should never report an XML declaration (XML 1.0,
section 2.8) or a text declaration (XML 1.0, section 4.3.1) using
this method.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4501' xml:id='l2h-4501' class="method">skippedEntity</tt></b>(</nobr></td>
<td><var>name</var>)</td></tr></table></dt>
<dd>
Receive notification of a skipped entity.
<P>
The Parser will invoke this method once for each entity
skipped. Non-validating processors may skip entities if they have
not seen the declarations (because, for example, the entity was
declared in an external DTD subset). All processors may skip
external entities, depending on the values of the
<code>feature_external_ges</code> and the
<code>feature_external_pes</code> properties.
</dl>
<P>
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