Re: [csswg-drafts] [css-cascade][css-syntax] New `!revertable` flag to mark a declaration as "can be reverted when IACVT" (#10443)

Good question! For registered custom properties, things should be relatively straightforward and work as for any other custom properties. In your example it will be `0`, as no `--registered` is defined with a valid value, and if we will have something like:

```CSS
.example {
  --registered: 1;
  --IACVT: max(invalid);
  --registered: var(--IACVT) !revertable;
}
```

then it will revert to `1`.

For unregistered custom properties, the most logical thing to do is to treat them as they're treated now: always valid until used, in the same way it currently “taints” any declaration making fallbacks impossible (and for which we'll have `first-valid()` — https://github.com/w3c/csswg-drafts/issues/5055).

I don't know if it is currently possible to determine if an unregistered custom property is invalid _before_ using it? If so, I can see it useful to be able to revert to previous values when doing `!revertable`. Otherwise it will be useless, and making it work this way should not break anything, as `!revertable` is itself new, so we can define how it works for this case (again, if this is technically possible/feasible).

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Received on Thursday, 10 October 2024 18:48:35 UTC