Am Wed, 1 Oct 2014 16:46:13 +0200 schrieb
[log in to unmask]:

>> It is normally not the *key* that is required but a *value*
> 
> Except if some keys are considered as mandatory arguments (and they
> could not be turned into arguments because keys are much more explicit
> than arguments).

No, it is still the value you want. E.g assume that beside your keys
you also define a key numbermonth=143/6 and a key
numberdate=143/6/2014 and a key extranumber=143/b and a key
issuenumber as alias to number. All set the needed value 143. 

So which key do you want to declare as required? 


>> Imho it is easier and more logical to test for the value and emit an
>> error if is doesn't exist.
 
> OK but, AFAICS, there isn't any high level key property for this (and
> that's the point of this thread): 

The question is if the high level key property is the correct place
to declare such a requirement on a value. 

>> (Actually I wouldn't emit an error. As almost everyone is using
>> scrollmode today error message are often ignored.
 
> Most of the TeX editors highlight errors, no? At least it is the case
> for TeXstudio, for instance.

Sure but a lot of users tend to ignore them as long as the document
compiles. They often don't understand what the error means and so
turn a blind eye on it. You wouldn't believe how many people start
the correct errors only when the 100-error limit is reached and
nothing works ;-)



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