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Date:         Tue, 25 Aug 2015 00:11:38 +0200
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From: Bruno Le Floch <blflatex@GMAIL.COM>
Subject: Re: Catcode changes
To: LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
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Status: R

On 8/24/15, Joseph Wright <joseph.wright@morningstar2.co.uk> wrote:
> On 25/08/2015 01:33, aparsloe wrote:
>> It has taken me a while to get to grips with \tl_set_rescan:Nnn <tl var>
>> {setup} {tokens}, not least the fact that *omission* from the setup
>> means "revert to usual catcode". I think this is worth documenting in
>> interface3.pdf, since it seems not unreasonable (at least it did to me)
>> to suppose that if one has explicitly changed a catcode using
>> \tl_set_rescan:Nnn, only a similarly explicit change would revert the
>> catcode to its usual value. In particular it would be helpful to
>> document the fact that using an empty setup { } reverts everything to
>> usual values.
>>
>> Andrew
>
> I see what you mean: I'll add a note that any chars not set up
> explicitly will have the *current* catcode applied. (That's not quite
> the same as saying the 'usual' value.)
>
> Worth noting perhaps that rescanning tokens is in general a bit tricky
> to use safely. (Certainly if possible I find other ways of solving
> problems.)

(Off-list to avoid noise.)
If you do change the doc, please include a comment along those lines
(that rescanning is typically not the best approach).

Bruno