Add a note regarding media attribute mismatch

[yoavweiss]

At https://bugs.chromium.org/p/chromium/issues/detail?id=792038, the conclusion was that a note regarding the behavior in case media doesn't match the environment is required.
This adds such a note.

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[igrigorik]

This is a bit odd to me, as there is nothing preload specific here and this is precisely how media is specced and intended to be used. That said, OK, I guess.

[yoavweiss]

I don't disagree, but people did get confused by this, and adding notes is easy :) I believe the reason for confusion is that for rel=stylesheet, links do fetch resources, even if in lower priority.

[scottjehl]

Agreed, @yoavweiss. It'd be interesting if link[rel=stylesheet] didn't fetch until its media matches, but I don't know of any browsers that do that. Thanks!

[yoavweiss]

Agreed, @yoavweiss. It'd be interesting if link[rel=stylesheet] didn't fetch until its media matches, but I don't know of any browsers that do that. Thanks!

I believe that's not web-compatible, as too many sites break as a result (at least that was the case last time it was tried, by Opera IIRC).

Maybe @zcorpan would know more of the history there.

[zcorpan]

Probably there were sites accessing the cssom or so, don't recall exactly