The Infoset is priceless for modelling the surface syntax. For everything else there's RDF.
btw, twisty discovery there, some see alsos - a couple of hours ago I posted a comment to mnot's blog re. his post on XML Infoset, RDF and Data Modelling. Indirectly (via Planet RDF) I just found James Tauber's response to an earlier post from mnot on the same subject, which includes the gem above.[Danny]