XML::Twig - Tree interface to XML documents allowing chunk by chunk
processing of huge documents.

From the website:

  XML-Twig is a Perl module that subclasses XML-Parser to allow easy
  processing of XML documents of all sizes.  A flush method allows dumping of
  a completely processed sub-document to be printed, thus allowing processing
  of documents of any size.

See also: http://www.xmltwig.com/