Re: [csswg-drafts] [css-values-5] Maybe min, max and step should not be part of the random-caching-key (#11742)

Definitely `random()` shouldn't infer a caching key from its source declaration. But I think we can and should give it maximum randomness unless the author explicitly ties things together.

Randomness needs to resolve at computed-value time. That's required for it to inherit sensibly.

Given that, I think each `random()` instance (unless otherwise specified by the author) should compute independently. If you specify the same `random()` function twice in a single property on a single element, or on two different properties, or on two different elements, they would compute to different values. Essentially, if you don't specify a caching key, we throw in the property name, an index (this is the Nth `random()` in the value), and the element identity as the caching key.

Then if the author wants to tie things together, they can do that explicitly. Two `random()` functions compute to the same value if they share an identifier, with `per-element` essentially subbing in the element's identity. So `random(--foo, 1, 10)` always computes to the same value across the entire page; and `random(per-element, 1, 10)` always computes to the same value on a single element, but different values on different elements; and `random(per-element --foo, 1, 10)` computes differently than `random(per-element --bar, 1, 10)`.

Yes, that means registered custom properties behave differently because they compute things up front. But that's already true, [as you point out](https://github.com/w3c/csswg-drafts/issues/11742#issuecomment-2679931790).

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The one other thing to be careful of is shorthand properties. We _probably_ want `margin: random(1, 10)` to resolve to the same random value on all four sides simply because if we don't, then splitting a property into longhands later becomes problematic. (Also it's a reasonable expectation for shorthands, to duplicate the value.) We can solve this by saying that `random()` is keyed to a property before shorthand expansion.

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Received on Wednesday, 5 March 2025 22:39:42 UTC