First, thanks for the comments :--) You can also have a look at the tutorial, which seems to be the easiest way to grok the module for most people, as the POD is really more of a reference, at 2500 lines.

how hard is it to get Twig to validate as well as parse?

Rather hard actually. I could add (yet another!) option to use XML::Checker instead of XML::Parser, but I am not sure I trust it completely. So the easiest way is probably to install libxml2 and to use xmllint --valid on the output file.