[csswg-drafts] [css-backgrounds-3] Can `background` syntax be made more future-proof? (#12849)

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

== [css-backgrounds-3] Can `background` syntax be made more future-proof? ==
I hope this editorial change can be applied to [`<final-bg-layer>`](https://drafts.csswg.org/css-backgrounds-3/#typedef-final-bg-layer) in CSS Backgrounds 3:

```diff
background = <bg-layer>#? , <final-bg-layer>

- <final-bg-layer> = <bg-image> || <bg-position> [/ <bg-size>]? || <repeat-style> || <attachment> || <visual-box> || <visual-box> || <'background-color'>`
+ <final-bg-layer> = <'background-image'> || <'background-position'> [/ <'background-size'>]? || <'background-repeat'> || <'background-attachment'> || <'background-origin'> || <'background-clip'> || <'background-color'>`
```

Basically the same change (omitted for brevity) would apply to `<bg-layer>`.

**Why?**

(1) [`background-clip`](https://drafts.csswg.org/css-backgrounds-4/#background-clip) is defined with `<bg-clip>` in CSS Backgrounds 4, which produces `<visual-box> | [ border-area || text ]`. But `<*-bg-layer*>` in CSS Backgrounds 3 only accepts `<visual-box>`. By using property value ranges (`<'background-*>`) instead of specific types (`<bg-*>`), the `background` syntax can be decoupled from longhand or type definitions in specific level(s) of the spec.

(2) CSS Backgrounds 4 editors could extend `background-repeat` without changing `<repeat-style>` (which is used in `mask` syntax) or creating `<bg-repeat>`. The same applies to `background-attachment` and `<attachment>`, which is however not used elsewhere.

(3) `<final-bg-layer>` mixes `<'background-color'>` and `<bg-*>`, which seems inconsitent.

(4) `... || <'background-origin'> || <'background-clip'> || ...` helps explaining in which positions are expected the corresponding longhand values.

Optionally, `<bg-image>`, `<bg-position>`, `<bg-size>`, could be dropped.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/12849 using your GitHub account


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Received on Wednesday, 24 September 2025 07:24:27 UTC