[css-color-3] opacity should use <<number>> not <<alphavalue>> “which is syntactically a <<number>>”

[fantasai]

The value of opacity looks and behaves exactly as a <<number>>. It should be defined as actually being a <<number>>, so that it's clear. This will hook into future specs like Animations more correctly.

This should just be an editorial change.

[svgeesus]

I think that comment also applies to CSS Color 4 definition of opacity

This would be an erratum on Color 3, but an editorial change on Color 4.

[tabatkins]

I'm fine with killing <alphavalue>, but note that it's now equivalent to <number> | <percentage>, not just <number>.

[AmeliaBR]

Note that SVG 2 currently references the <alphavalue> type for various properties. So if you decide to kill it, please make sure that an issue (or ideally a PR) gets filed on SVG to match up.

But I do agree that, since the limits on the value are not enforced by the parser, it is grammatically simpler to just use the raw data types. The benefit of having a designated type really only comes in when you start trying to parse the syntax for the color functions, where it helps explain the meaning of the value.

[svgeesus]

The benefit of having a designated type really only comes in when you start trying to parse the syntax for the color functions, where it helps explain the meaning of the value.

Yes, I thought that was the point. I hadn't realized it would somehow affect the animation spec (and don't understand why it would).

[svgeesus]

It seems desirable (for readability, for cross-spec linking and consistency) to say that something is an <alphavalue.. Can't we just (continue to) define the term, and the definition is <number> | <percentage> ? Would that still work for animation to be correctly defined?

[svgeesus]

ping @fantasai @tabatkins @AmeliaBR do we:

1. remove <alphavalue> and replace it with <number> | <percentage>
2. define <alphavalue> as <number> | <percentage> (and do what to make animations work)?

I'd like to close off this issue, get Color 4 updated and Color 3 errata'ed.

[svgeesus]

re-ping @fantasai @tabatkins @AmeliaBR

[AmeliaBR]

I don't see any problem with continuing to define <alphavalue> as an intermediate syntax for the specs. Animations should still be fine.

The fact that it is now a union of two types makes it much more useful to continue to have a shorthand syntax.