[perl-xml-cvs] CVS: perl-xml-faq perl-xml-faq.xml,1.23,1.24

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Update of /cvsroot/perl-xml/perl-xml-faq
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv16337

Modified Files:
	perl-xml-faq.xml 
Log Message:
- add Q&A re namespaces and XPath

Index: perl-xml-faq.xml
===================================================================
RCS file: /cvsroot/perl-xml/perl-xml-faq/perl-xml-faq.xml,v
retrieving revision 1.23
retrieving revision 1.24
diff -u -d -r1.23 -r1.24

--- perl-xml-faq.xml	23 Oct 2006 02:54:34 -0000	1.23
+++ perl-xml-faq.xml	6 Nov 2006 08:26:32 -0000	1.24
@@ -19,6 +19,7 @@
     <year>2003</year>
     <year>2004</year>
     <year>2005</year>
+    <year>2006</year>
     <holder>Grant McLean</holder>
   </copyright>
 
@@ -2332,6 +2333,103 @@
     </answer>
   </qandaentry>
 
+  <qandaentry id="namespaces_xpath">
+    <question>
+      <para>Using XPath with Namespaces</para>
+    </question>
+    <answer>
+
+      <para>People often experience difficulty getting their XPath expressions
+      to match when they first use <classname>XML::LibXML</classname> to
+      process an XML document containing namespaces.  For example, consider
+      this XHTML document with an embedded SVG section:</para>
+
+      <programlisting><![CDATA[
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
+    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head>
+  <title>Sample Document</title>
+</head>
+<body>
+
+<h1>An HTML Heading</h1>
+
+<s:svg xmlns:s="http://www.w3.org/2000/svg" width="300" height="200">
+  <s:rect style="fill: #eeeeee; stroke: #000000; stroke-width: 1;"
+    width="80" height="30" x="60" y="50" />
+  <s:text style="font-size: 12px; fill: #000066; font-family: sans-serif;"
+    x="70" y="70">Label One</s:text>
+</s:svg>
+
+</body>
+</html>
+      ]]></programlisting>
+
+      <para>The elements in the SVG section each use the namespace prefix
+      's' which is bound to the URI 'http://www.w3.org/2000/svg'.  The
+      prefix 's' is completely arbitrary and is merely a mechanism for 
+      associating the URI with the elements.  As a programmer, you will
+      perform matches against namespace URIs not prefixes.</para>
+
+      <para>The elements in the XHTML wrapper do not have namespace prefixes,
+      but are bound to the URI 'http://www.w3.org/1999/xhtml' by way of the
+      default namespace declaration on the opening &lt;html&gt; tag.</para>
+
+      <para>You might expect that you could match all the 'h1' elements using
+      this XPath expression ...</para>
+
+      <programlisting><![CDATA[
+//h1
+      ]]></programlisting>
+
+      <para>... however, that won't work since the namespace URI is effectively
+      part of the name of the element you're trying to match.</para>
+
+      <para>One approach would be to fashion an XPath query which ignored the
+      namespace portion of element names and matched only on the 'local name'
+      portion.  For example:</para>
+
+      <programlisting><![CDATA[
+//*[local-name() = 'h1']
+      ]]></programlisting>
+
+      <para>A better approach is to match the namespace portion as well.  To
+      achieve that, the first step is to use
+      <classname>XML::LibXML::XPathContext</classname> to declare a namespace
+      prefix.  Then, the prefix can be used in the XPath expression:</para>
+
+      <programlisting><![CDATA[
+my $parser = XML::LibXML->new();
+my $doc    = $parser->parse_file('sample.xhtml');
+
+my $xpc = XML::LibXML::XPathContext->new($doc);
+$xpc->registerNs(xhtml => 'http://www.w3.org/1999/xhtml');
+
+foreach my $node ($xpc->findnodes('//xhtml:h1')) {
+  print $node->to_literal, "\n";
+}
+      ]]></programlisting>
+
+      <para>The same technique can be used to match 'text' elements in the 
+      SVG section:</para>
+
+      <programlisting><![CDATA[
+$xpc->registerNs(svg => 'http://www.w3.org/2000/svg');
+foreach my $node ($xpc->findnodes('//svg:text')) {
+  print $node->to_literal, "\n";
+}
+      ]]></programlisting>
+
+      <note><para>The <classname>XML::LibXML::XPathContext</classname> module
+      has been included in the <classname>XML::LibXML</classname> distribution
+      since version 1.61.  Prior to that it was in its own separate
+      distribution on CPAN.</para></note>
+
+    </answer>
+  </qandaentry>
+
 </qandadiv>
 
 <qandadiv id="misc"><title>Miscellaneous</title>



