[css-values] attr() banning type(<url>) is kind of arbitrary.

[emilio]

https://drafts.csswg.org/css-values-5/#typedef-attr-type has this bit:

For this purpose, <url> is invalid as a <syntax-single-component>. Values that fail to parse according to the syntax trigger fallback.

But that seems fairly arbitrary? If only, because it also doesn't forbid <image>, which can also parse URLs.

I think the tainting works regardless, so why do we need this?

Looking at interop tests, Safari and Gecko don't implement this right now.

cc @tabatkins @andruud @dshin-moz @weinig

[emilio]

I guess we need to decide either:

• Keep banning <url> and additionally ban <image> maybe?
• Lift that restriction altogether.

Hopefully an easy call?

[Crissov]

The former would not suffice since there are other cases where a <string> is treated as an URL without (or in addition to) referencing <url> or <image>, e.g. within image-set().

[emilio]

That's my point, the tainting catches that but at that point why banning <url>?

[emilio]

@astearns: I think this might be good enough for an async resolution, I propose to remove that restriction.

[astearns]

Let’s get a Blink comment here first, since it sounds like it would be a change for them