We need a way to do:

<tdml:infoset file="...."/>

This is to support large infosets where you really don't want them cluttering up the TDML, but also if we look at the materials in github DFDLSchemas, IBM folks have been putting the data in TestData subdirs, and the expected result infoset XML in TestInfoset subdirs. It would be good to not have to repeat these infosets as XML in the TDML files.