[css3-conditional] @supports rule

[svgeesus]

from https://lists.w3.org/Archives/Public/www-style/2018Jan/0087.html raised by Dennis Heuer

if I read well, the rule @supports is only taking single properties as
arguments. I'd like to see it support css version and spec names to
allow enframing the case more widely, like:

@supports css21 and (css3: text-decoration, compositing, transform) ...

This is a quite arbitrary example... Just a guess...

[svgeesus]

from https://lists.w3.org/Archives/Public/www-style/2018Jan/0090.html rejected by @tabatkins

As previous emails have explained, CSS is not versioned.

As for providing an entire spec name, that's problematic for a few reasons.

1. Some spec names overlap with property names, like "transform".

2. Spec names are intended to be human-only; we didn't choose their
   names with the intention to show up in APIs.

3. Most importantly, the @supports rule is very intentionally designed
   to rely solely on existing parsing machinery, rather than
   human-maintained lists. To evaluate a support condition, all a
   browser has to do is feed the property+value to their CSS parser and
   see if it parses or not. This system avoids the failure modes of
   previous attempts at providing an "is this supported?" API, namely
   that a human-maintained set of features is often out of date or
   encourages lying. These problems made the legacy hasFeature() JS API
   mostly useless, for example. Allowing an author to ask "is this
   entire spec supported?" falls exactly into that failure mode.