XML::LibXML::Document has a toString() method that converts the parsed DOM into a string, including all the child nodes. It has an optional format parameter, which, when set to zero "...the document is dumped as it was originally parsed".
Depending on how lazy / strict you're feeling you could either:
- just serialize each document into a string and use (anchored) regexes to strip off the document root
- use the documentElement() method to get the root of each document, then loop through its childNodes array, and individually toString() each of those
I'd be surprised if there isn't an XML::Twig equivalent to that - I'm just personally much more familiar XML::LibXML - hope that helps.