Re: @else in Media Queries

On Fri, Jun 10, 2016 at 2:53 AM, Mark Brown <[email protected]> wrote:
> On Fri, Jun 10, 2016 at 6:58 AM, Tab Atkins Jr. <[email protected]> wrote:
>> On Thu, Jun 9, 2016 at 3:34 AM, Daniel Glazman <[email protected]> wrote:
>>> My recommendation for @else is then the following: yes to @else but
>>> we need to have boolean completion in MQs first, to be able to
>>> serialize precisely the MQ relevant to a given style rule. That means
>>> allowing negated single media features, OR operations and grouping
>>> through parentheses. I'm pretty sure we'll have requests for that (if
>>> we don't have them yet) anyway.
>>
>> We already have all of those.
>
> Well, not quite. Florian's example on the issue tracker [1]
> illustrates that you can't always write a separate condition that's
> equivalent to an else, because of how unknown media features are
> handled.
>
> To make the set of operations complete, you could, for example, add a
> function such as 'unknown(media-query)' which is true iff its argument
> evaluates to unknown. So this doesn't seem a major hurdle.

I'm not sure that's what Daniel was referring to; his email *seemed*
to be just about NOT/AND/OR, which does indeed exist already for
@media and @supports.

I haven't seen a use-case yet for needing to explicitly test for
unknown values, except "emulate what @else can do".  If we can come up
with one we can always add such a function.

~TJ