[csswg-drafts] [font-loading] How should invalid font resources fail?

RByers has just created a new issue for 
https://github.com/w3c/csswg-drafts:

== [font-loading] How should invalid font resources fail? ==
The [load 
algorithm](https://drafts.csswg.org/css-font-loading/#font-face-load) 
is a little vague on whether or not it's an error to successfully load
 a resource which is not a valid font (and I don't see any tests in 
csswg-test for this spec to help clarify the expectation here).  I 
assume we wouldn't want to have a FontFace instance for something that
 doesn't represent a valid font, and so it should be an error - but 
the spec should probably call that out explicitly.

This come up in the [review of this web-platform-test 
change](https://github.com/w3c/web-platform-tests/pull/4378).

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/852 using your GitHub 
account