I’ve been wondering this too! Nothing I’ve done seems to work.
Only downside I’ve found to the new way.
Poking through the source, I note that the form_tag method uses the
concat method if a block is given, which looks like it ends up writing
directly to _erbout (via an eval call - which would seem to be an overly
slow way of going about it…) Absent a quick redef of that method
around the form_tag call, I don’t see a way to use form_tag inside a