This (required) test uses DTD validation in a p:load step.

The text

"It is a dynamic error (err:XC0027) if the document is not valid or the step doesn't support DTD validation."

suggests that a conformant processor may not necessarily support DTD validation.  If that is true:

1.  This test should be moved into the optional folder.
2.  DTD validation should be noted as an implementation-defined feature.