A common mistake is to import a DFDL schema that has a dfdl:format in it, thinking that is all you have to do in order to make that format work for you.

That actually accomplishes nothing. The dfdl:format annotation of an imported/included DFDL schema has no influence on the file importing/including it.

So the original DFDL schema doing the include/import actually has no dfdl:format annotation in effect.

But the error you get is something like "alignment property undefined" or something.

If there is no default format, the message should not just say that the property it needs is not found, but should point out that there was no default format specified where it could have found it.

Something like:
"The alignment property was not found.
....file and line number informatino about where it is needed....

Note: there is no default format in this schema file. That is, no dfdl:format annotation at the top level of the schema file."

It is these last two lines that need to be added.

Alternatively, we could just warn that there is no default format in any given schema file, but that could be misleading since some schema files exist only to provide named format definitions, so this message would be spurious.