Hi,
>
> In fact one could think of also having
>
> \<thing>_case:nnTF
>
> where the T branch is selected if you have a match (in addition to
> executing any match code from the "n" argument).
This sounds more logical for me and I really like this idea. I think the
true part is mostly a message instead of a function. However for me as a
beginner it's more consistent in a expl3 manner. ;-)
So after this small discuss I vote for the following:
\<thing>_case:nn_p
\<thing>_case:nnF
\<thing>_case:nnT
\<thing>_case:nnTF
Best regards
Marco