If you write a TDML file and it uses an external schema file, then that schema can include/import other schemas.

If you use the tdml:defineSchema element to embed the schema directly, then include/import do not seem to work.

This is bad because to make a nice compact TDML file as a bug report, you will want to avoid having to put lots of default format properties in it. You'll just want to include one of the built-in format defaults (IBMdefined/GeneralPurposeFormat.xsd, or some other).