I'm new in XML processing (really i'm new quite on everithing!) but I remember a 13 factor when the twig is created.

I found also this speed comparison you could find interesting.
The summaized results are:

If you want high performance: XML::Parser
If you want relatively easy, memory efficient parsing of huge files: XML::Twig
If you want easy-to-implement for small files: XML::Simple
If you want to have a bad deal: XML::Smart

L*