Am 07.07.2013 19:10, schrieb Marco Daniel:
> 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#

something  _p:... is only supported if the we deal with true predicates 
that do not have side effects and are expandable. In other words not 
everything that has a TF variant also exists as a predicate