Module: LibXML::XML::XPath

The XPath module is used to query ::LibXML::XML documents. It is usually accessed via the Document#find or Node#find methods. For example:

document.find('/foo', namespaces) -> XML::XPath::Object

The optional namespaces parameter can be a string, array or hash table.

document.find('/foo', 'xlink:http://www.w3.org/1999/xlink')
document.find('/foo', ['xlink:http://www.w3.org/1999/xlink',
                       'xi:http://www.w3.org/2001/XInclude')
document.find('/foo', 'xlink' => 'http://www.w3.org/1999/xlink',
                          'xi' => 'http://www.w3.org/2001/XInclude')

Working With Default Namespaces

Finding namespaced elements and attributes can be tricky. Lets work through an example of a document with a default namespace:

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
  <title type="text">Phil Bogle's Contacts</title>
</feed>

To find nodes you must define the atom namespace for libxml. One way to do this is:

node = doc.find('atom:title', 'atom:http://www.w3.org/2005/Atom')

Alternatively, you can register the default namespace like this:

doc.root.namespaces.default_prefix = 'atom'
node = doc.find('atom:title')

More Complex Namespace Examples

Lets work through some more complex examples using the following xml document:

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <getManufacturerNamesResponse xmlns="http://services.somewhere.com">
      <IDAndNameList xmlns="http://services.somewhere.com">
        <ns1:IdAndName xmlns:ns1="http://domain.somewhere.com"/>
      </IDAndNameList>
    </getManufacturerNamesResponse>
  </soap:Body>
</soap:Envelope>

# Since the soap namespace is defined on the root
# node we can directly use it.
doc.find('/soap:Envelope')

# Since the ns1 namespace is not defined on the root node
# we have to first register it with the xpath engine.
doc.find('//ns1:IdAndName',
         'ns1:http://domain.somewhere.com')

# Since the getManufacturerNamesResponse element uses a default
# namespace we first have to give it a prefix and register
# it with the xpath engine.
doc.find('//ns:getManufacturerNamesResponse',
          'ns:http://services.somewhere.com')

# Here is an example showing a complex namespace aware
# xpath expression.
doc.find('/soap:Envelope/soap:Body/ns0:getManufacturerNamesResponse/ns0:IDAndNameList/ns1:IdAndName',
['ns0:http://services.somewhere.com', 'ns1:http://domain.somewhere.com'])