> Thus document commands define the user syntax for some particular
> implementation, but for variants you'd do
>
> \NewDocumentCommand \fooa { ... } {
>   \internal_function:nnn ....
> }
> \NewDocumentCommand \foob { ... } {
>   \internal_function:nnn +++
> }
>
> with different argument mappings.

It makes perfect sense, thank you :).

-- 
Bruno