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Message-ID:  <10k836fpz0maa.dlg@nililand.de>
Date:         Wed, 1 Oct 2014 15:18:57 +0200
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From: Ulrike Fischer <news3@NILILAND.DE>
Subject: Re: [l3keys] Suggestion: Add a key property for specifying key that /has/ to be used
To: LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
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Status: R

Am Tue, 30 Sep 2014 19:00:52 +0200 schrieb
denis.bitouze@LMPA.UNIV-LITTORAL.FR:

> In the use case I have in mind, `key' would be required and expect an
> integer. Would it be missing, an error message would be emitted; would
> its value be anything but an integer, an(other) error message would be
> emitted.

It is normally not the *key* that is required but a *value* and
there is no one-to-one relation between keys and values: e.g. in
geometry you can set the left margins through the keys hmargin,
margin, implicitly when you set other width etc.

So a key property .required would be senseful only for "basic keys"
and you would have to be very careful that you use these basic key
if you set the value with other keys too.

Imho it is easier and more logical to test for the value and emit an
error if is doesn't exist.

(Actually I wouldn't emit an error. As almost everyone is using
scrollmode today error message are often ignored.  I would give the
issue number a default value of a {\Huge\color{red}XXXXXXX})

-- 
Ulrike Fischer 
http://www.troubleshooting-tex.de/