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            <zqejj1e7vcjn$.dlg@nililand.de> <m34mvnre7x.fsf@example.com>
            <1p1jnnjmq41l6.dlg@nililand.de> <542D37EA.1080101@free.fr>
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Date:         Thu, 2 Oct 2014 16:45:19 +0200
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From: =?utf-8?Q?Denis_Bitouz=C3=A9?=
              <denis.bitouze@LMPA.UNIV-LITTORAL.FR>
Subject: Re: [l3keys] Suggestion: Add a key property for specifying key that /has/ to be used
To: LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
In-Reply-To:  <542D37EA.1080101@free.fr> (Julien RIVAUD's message of "Thu, 2
              Oct 2014 13:32:58 +0200")
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Le 02/10/14 à 13h32, "Julien RIVAUD (_FrnchFrgg_)"
<frnchfrgg-qbkUeYn5DSc@public.gmane.org> a écrit :

> Le 02/10/2014 09:22, Ulrike Fischer a écrit :
>
>> Beside this there is also the timing problem Joseph mentioned: when
>> should be tested if a key has been used? It is obviously not the key
>> code of the key that can do it. So imho you are not looking for a
>> .required property but a .enableifsettest property which adds and
>> sets some boolean which you can later check.
>
> Or better yet, use an initial value for your property that unambiguously
> represents "not set", and validate that at the beginning.
>
> Since you need to have an extra step to check if the required properties have
> been set, you can as well use a token list to store the value instead of
> directly an int for instance, and first check if it is your special "not set"
> value, then cast it to integer yourself.

Indeed. Maybe I was wrong, but it came to my mind that I wouldn't be the
only one who needs such checks. And, instead of leaving each one hacking
this by hands more or less properly, a general LaTeX3 frame could be
useful.
-- 
Denis