Latin Pro: tdieresis?

In the GF glyph lists there is a `tdieresis` (Latin Pro) and `tdieresis.sc` (Latin Expert) but no majuscule form. I understand that this is due to the fact that the majuscule does not have unicode point, but was curious how it plays out when being used.

I tested in InDesign the encoded `tdieresis` and a `t` followed by `dieresiscomb`; the latter works as expected when set to all caps, but the former does not change case. Would it make sense to add a substitution in the feature code? or is that not necessary?

Start by reviewing the GF glyph list entries for `tdieresis` and `tdieresis.sc`, then examine the referenced feature code and the InDesign behavior described in the issue. Determine whether a substitution is needed for all-caps use and document or implement the agreed behavior. Done means the case-conversion behavior and any required feature-code change are verified.

Written by the indexing model from the issue text.