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Date:         Mon, 16 May 2011 14:11:53 +0930
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From: Will Robertson <wspr81@GMAIL.COM>
Subject: Re: xparse and space skipping
To: LATEX-L@listserv.uni-heidelberg.de
In-Reply-To:  <19920.15087.714131.100464@morse.mittelbach-online.de>
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Status: R

On 16/05/2011, at 6:13 AM, Frank Mittelbach wrote:

> Now one could argue that that this  behavior for \\ is useful (especially in
> math for which amsmath reimplements it) but realistically what are the other
> places that need this kind of behavior?

This is a better point than any that I made :)

[snip]

> There would still be the question of control symbols viz control words. By
> default a control symbol (e.g., \? \/ ...) will not skip spaces and \\
> actually explicitly has code to scan and ignore spaces so was deliberately put
> into the command class by Leslie to get a consistent interface for his main
> commands (and amsmath changed it back).
> 
> But I find a single exception (if implemented) still preferable to the other
> options.

Okay, I'm happy with this. We should revert back to space-skipping behaviour; only question is what to do about control symbols? Practically, there are only a handful that you'd expect to see defined to take an optional argument, perhaps \\ and \+ and anything else a user wants to (re-)define.

If we choose space-skipping then we're consistent with 2e; if not we're consistent with amsmath. I tend toward the latter but would also be happy to have \\ as a special case instead and go with the former.

Cheers,
-- Will