- From: Jan Varga via GitHub <noreply@w3.org>
- Date: Thu, 19 Mar 2026 15:41:49 +0000
- To: public-css-archive@w3.org
janvarga has just created a new issue for https://github.com/w3c/csswg-drafts:
== [css-typed-om-1] Should partial reification of list-valued properties be allowed? ==
It is not entirely clear how CSS Typed OM Level 1 intends list-valued properties to behave when only some iterations are representable.
Example:
```js
const el = document.createElement("div");
el.style.transitionTimingFunction = "linear, ease";
console.log(el.attributeStyleMap.getAll("transition-timing-function"));
// [CSSKeywordValue("linear"), CSSKeywordValue("ease")]
el.style.transitionTimingFunction = "linear, step-start";
console.log(el.attributeStyleMap.getAll("transition-timing-function"));
// [CSSStyleValue] (single property-tied unsupported value)
```
In the second case, `step-start` may be canonicalized to `steps(1, start)`, which is not representable in Typed OM Level 1.
The spec text in §5.2 (“Unrepresentable Values”) says:
> “When this is the case, the property is reified as a CSSStyleValue for a particular property...”
This suggests an all-or-nothing behavior at the property level.
However, list-valued properties are otherwise processed per-item (e.g. via `getAll()`), which makes it unclear whether partial reification should be allowed.
Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/13687 using your GitHub account
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Received on Thursday, 19 March 2026 15:41:50 UTC