[csswg-drafts] [css-backgrounds] Always serialize 'background-size' and `mask-size` as two values (#7802)

zcorpan has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-backgrounds] Always serialize 'background-size' and `mask-size` as two values ==
See https://github.com/whatwg/compat/issues/28

That change is now implemented in WebKit: https://github.com/WebKit/WebKit/pull/3372

Relevant CSS specs: https://drafts.csswg.org/css-backgrounds-3/#background-size and https://drafts.csswg.org/cssom/#serialize-a-css-value

@pxlcoder asked

> Do we have consensus from other engines on:
>
> Always serialize `background-size` as two values.

CSSOM says

> * If component values can be omitted or replaced with a shorter representation without changing the meaning of the value, omit/replace them.
>
> * If either of the above syntactic translations would be less backwards-compatible, do not perform them.

The last bullet point seems to apply here, as it impacts `-webkit-background-size` if implemented as a legacy shorthand. But maybe we can include each known property with special serialization, and what that serialization should be, so it's not ambiguous for those properties.

@pxlcoder also asked:

> Should we also change the serialization of mask-size to always use two values, for consistency?

Since `mask-size` also has a [`-webkit-` prefixed variant](https://compat.spec.whatwg.org/#propdef--webkit-mask-size) and also [uses `<bg-size>#` value grammar](https://drafts.fxtf.org/css-masking-1/#propdef-mask-size), I think it makes sense to use the same serialization rule as for `background-size`.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/7802 using your GitHub account


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Received on Wednesday, 28 September 2022 08:46:29 UTC