Behavior of "unknown " media feature name/value

[mdubet]

Media Queries Level 3/4/5 have a consistent description of the way to handle unknown media feature name or unknown media feature value: transform the media query to not all.

An unknown or , or disallowed , results in the value "unknown". A whose value is "unknown" must be replaced with not all.

(quote from https://drafts.csswg.org/mediaqueries-5/#error-handling)

With the introduction of the new <general-enclosed> term in the grammar and the 3-valued logic evaluation, and the intention of allowing future-proof query matching in the case of unknown media feature, my understanting of the spec would be that:

• when one (or several) media feature name or value is unknown, and the complete media query is unknown, such as (width: foobar) (unkown value) or (foobar) (unknown name), it should be replaced with not all.
• when one (or several) media feature name or value is unknown, but the complete media query is either true or false, it should not be replaced such as (foobar: foobarvalue) or (color) (assuming color is true).

However, the WPT media queries tests rely on another behavior:

wpt/css/mediaqueries/resources/matchmedia-utils.js

Line 36 in 0028b5a

return match.media == query;

Even when the media query result is unknown, they don't expect it to be replaced by not all. Is this a bug ?

Current implementations

The implementations in Firefox and Chrome have different behaviors on this issue.

Firefox Developer Edition (v104):

> window.matchMedia("(scan: foobar)")
> MediaQueryList { media: "not all", matches: false, onchange: null }

> window.matchMedia("(foobar: none) or (color)")
> MediaQueryList { media: "not all", matches: false, onchange: null }

In Chrome Canary:

> window.matchMedia("(scan: foobar)")
> MediaQueryList {media: '(scan: foobar)', matches: false, onchange: null}

> window.matchMedia("(foobar: none) or (color)")
> MediaQueryList {media: '(foobar: none) or (color)', matches: true, onchange: null}

[gsnedders]

An unknown or , or disallowed , results in the value "unknown". A whose value is "unknown" must be replaced with not all.

(quote from https://drafts.csswg.org/mediaqueries-5/#error-handling)

w3c/csswg-drafts#7585 clarified the the spec text here:

An unknown <<mf-name>> or <<mf-value>>, or a feature value which does not matches the value syntax for that media feature, results in the value “unknown”. A <<media-query>> whose value is “unknown” must be replaced with ''not all''.

I think this makes it pretty clear that Firefox is right here? cc @andruud, given you changed away from this

[mdubet]

I think Firefox is right when the media query is unknown (1st example), but not when it's definitely true or false because of 3-value boolean logic (2nd example).

[gsnedders]

Oh, yeah, I guess there's still plenty unclear here: w3c/csswg-drafts#7595