[css-values-4] How does an empty url serialize?

[smfr]

https://drafts.csswg.org/css-values/#url-empty says how empty urls (url()) are resolved, but not how they are serialized.

Gecko serializes as url("about:invalid"), WebKit and Blink serialize as the resolved url (i.e. the base URL).

[smfr]

#2211 talked about this, and the IRC log says:

<fantasai> TabAtkins: Proposal is that the empty URL, rather than being treated as a relative URL, is treated as an invalid URL
<fantasai> TabAtkins: Computed value is still an empty string, just treated like 'about:invalid'

but the test css/css-values/urls/empty.html expects that the computed style is the the base URL. @gsnedders @emilio ?

[emilio]

Serializing to a valid URL like WebKit / Blink do seems wrong. If we do that then that breaks round-tripping.

I'm not in love with the about:invalid behavior, but I think it should be either that or serializing to url() / url("").

[gsnedders]

This is a duplicate of #6447

[smfr]

Closing as duplicate.