Behavior of "unknown " media feature name/value #35435
Description
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 withnot 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 istrue).
However, the WPT media queries tests rely on another behavior:
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}