TDML files are ordinary xml files, so you should be able to use default namespace prefixes to avoid the need to type prefixes. You should be able to do this in the usual ways.

Suppose however, you try to have the tdml namespace be the default at the top level of the schema, then inside the <tdml:defineSchema name="foo" xmlns="..."> you try to have the default namespace be that of xsd.

It doesn't work. It complains that an element inside the define schema has TWO xmlns attributes.

This has something to do with the way the TDML runner assembles an actual DFDL schema from the bits and pieces provided in the TDML file.

This problem is easily worked around. Move the xmlns to a more inner element, or just use prefixes. But the TDML runner is not correctly processing XML here.