TupleDesc for a Nested Record

Hi,

While returning from a function call, PL can easily interfere will be
returned HeapTuple's TupleDesc from fcinfo. But what if function returns
a record type? Then we must create our own TupleDesc (or AttInMetadata)
for the related attribute (and then create HeapTuple). So far everything
is ok, but how can I interfere the data types in the nested record? This
isn't supplied by fcinfo. What would you suggest in such a situation?

Regards.