XPath strangeness

Question

I'm writing a script which reads and manipulates a KML (xml) document. Below is a snippet of the document I'm reading:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Generated by Feature Manipulation Engine 2009 (Build 5658) -->
<kml xmlns="http://earth.google.com/kml/2.2" xmlns:atom="http://www.w3.org/2005/Atom"&gt;
    <Document>
        <name>South Australia</name>
        <visibility>1</visibility>
        <description><![CDATA[Statistical Local Area 2008]]></description>
        <Folder id="kml_ft_SA_SLA08">
            <name>SA_SLA08</name>
            <Placemark id="kml_1">
                <name>Mitcham (C) - West</name>
                <Style>
                    <!-- style info blah blah -->
                </Style>
                <Polygon>
                    <!-- blah blah -->
                </Polygon>
            </Placemark>

            <!-- snip lots more Placemarks -->
        </Folder>
    </Document>
</kml>

The problem I'm having is with using XPath to select anything from it!

$doc = new DOMDocument();
$doc->load('myfile.xml');    // returns true
$xp = new DOMXPath($doc);

$places = $xp->query("//Placemark");
echo $places->length;         // --> 0 ??!!??
$everything = $xp->query("//*"); // (so I know that the XPath isn't fully borked)
echo $everything->length;    // --> 2085

What's going on here?

Answer 1

<?php
$doc = new DOMDocument();
$doc->load('file.xml');    // returns true
$xp = new DOMXPath($doc);
$xp->registerNamespace('ge', 'http://earth.google.com/kml/2.2');

$places = $xp->query("//ge:Placemark");
echo $places->length;         // --> 0 ??!!??
$everything = $xp->query("//*"); // (so I know that the XPath isn't fully borked)

//echo $doc->saveXML();

Apparently you have to register the 'ge' namespace and query it as such, at least this is what I came up with after a few minutes googling. I guess sometimes we forget we're dealing with namespaces :p