On 21/02/2011 11:20, Bruno Le Floch wrote:
>> (I haven't looked into doing it non-expandably, which would be more robust.)
> My claim is that expandable is just as robust as non-expandable if
> - we have access to the full argument (i.e. no peeking ahead)
> - there is no token of catcode 1 other than a true "{"
> - there is no token of catcode 10 and character code other than 32 (space).

I suspect condition (2) is  killer. While assuming "{" is catcode 1 is
fine for LaTeX-like input, what happens if you're using LaTeX3 with some
other input syntax (for example XML)?
Joseph Wright