[cssom-1] [css-cascade] CSSImportRule.sheet not being null conflicts with @import supports()

[emilio]

https://drafts.csswg.org/css-cascade-5/#at-import:

Additionally, if a <supports-condition> blocks the application of the imported style sheet, the UA must not fetch the style sheet (unless it is loaded through some other link) and must return null for the import rule’s CSSImportRule.styleSheet value (even if it is loaded through some other link).

But https://drafts.csswg.org/cssom-1/#dom-cssimportrule-stylesheet is not nullable.

I think the fix is obvious (just make it nullable). Not sure if that needs a resolution tho?

[emilio]

@tabatkins @fantasai do you know if tweaking the OM spec to allow styleSheet to be nullable needs a resolution?

[tabatkins]

CSSOM is CR-level, so yes, normative changes need WG resolution. (But should be quick and easy.)

[SebastianZ]

@tabatkins CSSOM is still WD-level, not CR-level.

Sebastian

[css-meeting-bot]

The CSS Working Group just discussed [cssom-1] [css-cascade] CSSImportRule.sheet not being null conflicts with @import supports(), and agreed to the following:

• RESOLVED: Update CSSOM to allow null representation of imported style sheets

The full IRC log of that discussion

<fantasai> emilio: 2 specs conflicting with each other
<fantasai> ... imported stylesheets cannot be null, but since we have supports() condition the UA is not required to fetch the stylesheet
<fantasai> ... so we need CSSOM to allow it to be null
<TabAtkins> +1 for the obvious fix
<fantasai> +1
<fantasai> RESOLVED: Update CSSOM to allow null representation of imported style sheets