[css-typed-om-1] Should partial reification of list-valued properties be allowed?

[janvarga]

It is not entirely clear how CSS Typed OM Level 1 intends list-valued properties to behave when only some iterations are representable.

Example:

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.