Near identical answers :) some of which use http://www.w3.org/TR/xpath/#function-contains and some use perl regex (there are more answers if you click parent node)
xpather.pl
Re: Get Node Value from irregular XML (xpather.pl)
Re: Having trouble with siblings
Re^2: XML parsing and Lists
Re: Counting number of child nodes based on element value (typos)
Re^3: Extracting specific childnodes (xpath whitespace)
Re^3: Extracting specific childnodes (play xmllint --shell )
Re: How do i get value of an element if the next elememnt has specific value in XML::LibXML using Xpath?
Re: How do i get value of an element if the next elememnt has specific value in XML::LibXML using Xpath?
Re: How to parse xml with namespase vale in XMl:LibXML? ( XPath error : Undefined namespace prefix )
Re^2: How to parse xml with namespase vale in XMl:LibXML? (xmllint --shell setns / xpathtester)
http://stackoverflow.com/questions/17396974/libxml-looping-through-nodes-until

Also forget about XML::Parser its too low level. If you're tempted by that approach use XML::Twig :) it comes with many examples/tutorials / http://xmltwig.org/xmltwig/quick_ref.html, http://www.w3.org/TR/xpath/, Taking the Document Object Model (DOM) Approach to XML Documents - For Dummies, XPath Cheat Sheets | DevCheatSheet.com

sample html is book PathEnq - an XPath 2.0 editor, tester, debugger that also serves as a generic online XML analysis tool., PathEnq Screenshots, PathEnq Guide