Le 30/04/2013 16:06, Joseph Wright a écrit :
> Providing optional values is another question: we can tackle that a bit
> later (I hope).
>
> On where '-NoValue-' 'lives', the current approach is that it's an
> xparse-only concept as it's provided by xparse and so not available if
> you use
>
>      \RequirePackage{expl3}
>
> you can't use it.
I don't see that as a problem; the need currently only arises for users 
of xparse anyway.
Why cannot xparse provide both \IfNoValueTF and a public 
\xparse_if_no_value:n(TF) ?
> An alternative view is that it's a more general marker which can then be
> defined at the token list level, with a test
>
>      \tl_if_no_value:n(TF)
>
> [or similar: have to watch clash with \quark_if_no_value:n(TF)]. This
> test would then be a code level equivalent of \IfNoValue(TF).
It seems to me that the idea of a missing value only arises in cases 
where the input is not controlled (note that the low-level l3keys took 
another approach), as in user input via the LaTeX user interface; if 
some other packaqe one day needs to develop the same concept (say for 
file parsing) it would not be too late to add a function to the core 
kernel and make \xparse_if_no_value:n(TF) synonyms.

Cheers,

Julien "_FrnchFrgg_" Rivaud