CSS Nesting: The Nested Declarations Rule

[andruud]

Request for Mozilla Position on an Emerging Web Specification

• Specification title: CSS Nesting
• Specification or proposal URL (if available): https://drafts.csswg.org/css-nesting-1/#nested-declarations-rule
• Explainer URL (if available):
• Proposal author(s) (@-mention GitHub accounts): @fantasai et al.
• Caniuse.com URL (optional):
• Bugzilla URL (optional):
• Mozillians who can provide input (optional): @emilio
• WebKit standards-position: CSS Nesting: The Nested Declarations Rule WebKit/standards-positions#369

Other information

See also:

• The spec for the rule itself: https://drafts.csswg.org/css-nesting-1/#the-cssnestrule
• The new behavior for insertRule (step 4): https://drafts.csswg.org/cssom/#insert-a-css-rule
• Previous position for @nest: CSS Nesting: @nest #1013

[emilio]

I think the insertRule special-case is wrong, as per discussion... Parse declarations ~never fails (spec wise), it just returns an empty declaration list, so something like insertRule("yadayada") would not throw, just create an empty CSSNestedDeclarations object...

Easiest fix would be to check if the declaration list is not empty or so, though it seems that'd cause some other weird behavior like unknown-property: foo throwing, but unknown-property: foo; color: red working (and having a single declaration). I guess it's not too bad tho...

With that tweak or something along those lines resolved on by the CSSWG, this looks acceptable to me (kinda reluctantly).

I still think it's a really weird set-up, but given the discussions and that this is still better than the status quo, I guess positive is fine? Thanks for pushing this forward :)

[andruud]

I think the insertRule special-case is wrong

Yes, thanks, that was a mistake from my side.

(For the benefit of other people reading):

Easiest fix would be to check if the declaration list is not empty or so

Done: w3c/csswg-drafts#10519

Filed w3c/csswg-drafts#10520 to get a stamp for the above change, or to see if we should do something else instead.