Github user afs commented on the issue:
https://github.com/apache/jena/pull/473
On the question of mapping `ResultsFormat.FMT_TEXT`: IIRC it is because
text is only an output format and not an input format (but then CSV is also
only an output format).
When Jena 3.9.0 is completed, I can come back and look at this PR. In
principle, there is no reason not have have them extensible.
What syntax are you using for TSV extensions?---
