This definition appears very rarely
Why Would You Want Yet Another XML Parser? Expat and XML::Parser have proven themselves to be quite capable, but they are not without limitations. Expat was among the first XML parsers available and, as a result, its interfaces reflect the expectations of users at the time it was written. Expat and XML::Parser do not implement the Document Object Model, SAX, or XPath language interfaces (things that most modern XML users take for granted) because either the given interface did not exist or was still being heavily evaluated and not considered "standard" at the time it was written.