Joseph Wright skrev:
> Taking this idea, I'd probably favour something that doesn't include
> "xparse" as a document-level function: perhaps \ProcessedArgument or
> \ProcessingResult?

Yes, that is probably better.

> If I say that it will initially be a toks (for each
> parsing run), then you can do
>   \let\ProcessingResult\YourMacro
>   \def\ProcessingResult{whtever}
>   \toks_set:NV\ProcessingResult\Variable
> etc. Would that work?

Not sure what you're asking here. It wouldn't work to reset 
\ProcessingResult to \l_xparse_arg_toks only at the beginning of 
parsing the arguments of the command, as any processor can redefine it 
as a macro and then another can come along that expects it to be a toks 
register again; it would have to be reset before each processor.

Lars Hellström