User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Message-ID:  <m3k34m4vjd.fsf@somewhere.org>
Date:         Mon, 29 Sep 2014 11:37:26 +0200
Reply-To: Mailing list for the LaTeX3 project
              <LATEX-L@LISTSERV.UNI-HEIDELBERG.DE>
Sender: Mailing list for the LaTeX3 project <LATEX-L@LISTSERV.UNI-HEIDELBERG.DE>
From: =?utf-8?Q?Denis_Bitouz=C3=A9?=
              <denis.bitouze@LMPA.UNIV-LITTORAL.FR>
Subject: [l3keys] Suggestion: Add a key property for specifying key that /has/ to be used
To: LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
Precedence: list
Envelope-To: <rainer.schoepf@GMX.NET>
Status: R

Hi,

among others, `.value_forbidden:` and `.value_required:` key properties
from `l3keys` package are useful: they let us specify that a given key,
when used, either cannot or must receive a value.

What could be useful as well is a key property, say `.required:`, that would
specify that the corresponding key /has/ to be used. This could be helpful for
instance in the case of a document command `\MyModuleSetup` for setting up
a module `mymodule`:

    \DeclareDocumentCommand \MyModuleSetup { m }
      { \keys_set:nn { mymodule } { #1 } }

where some module property /has/ to be specified.

I know this can be achieved with something like test of existence of
some tokenlist and message emitted in case of nonexistence but a high
level key property for this could be nice.

May I ask what is your opinion about that?

Thanks in anticipation.
-- 
Denis