On 30/09/2014 19:00, Denis Bitouzé wrote:
>> At present, key properties mainly apply to individual keys in a 'stand
>> alone' sense. This request is different as it's actually about an entire
>> set of keys.
> 
> No, maybe I was unclear: my question concerned the "requireness" of
> a single (or maybe several but treated separately) key property.

I perhaps wasn't clear here. Other properties can be tested by examining
just the key itself, so for example

   foo .value_required:

is tested at the point you do

   foo = <value>

On the other hand, a requirement to set some key can only be tested at
the end of \keys_set:nn, once you know what keys were set. Moreover,
it's potentially ambiguous as

  \keys_set:nn { foo } { required = value }
  \keys_set:nn { foo } { other-key }

doesn't have the "required" key in the second setting: is it required
here or not?
--
Joseph Wright