Two "variants" of color-mix() ??

[svgeesus]

In CSS Values 5 I was astonished to read 5.3. Interpolated Color Values: the color-mix() notation

This specification extends the color-mix() functional notation as a mix notation accepting the following syntaxes:

<color-mix()> =
  color-mix( <progress> && <color-interpolation-method>?, <color>, <color> ) |
  color-mix( <color-interpolation-method>, [<color> && <percentage [0,100]>?]#{2} )

The used value of the first mix notation variant is equivalent to assigning the <progress> value, as a <percentage>, to the of the second <color> argument in the second variant. That is, color-mix(progress, color1, color2) is equivalent to color-mix(color1, color2 progress). See CSS Color 5 § 3 Mixing Colors: the color-mix() Function for the normative definition of the second variant.

Why is there a second "variant" of color-mix() defined, with zero discussion that I can recall, which is merely a permutation of the parameter order, and has zero tests in WPT, unlike the other "variant" which is widely implemented, with 1510 tests in WPT and part of Interop 2023?

[SebastianZ]

This was added in 0d8967a, which references the related discussions, especially #6245 (comment).
@fantasai can surely explain more. Though it looks like it was added as an initial draft for generalized interpolation functions while the discussion is still going on.

Sebastian

[tabatkins]

Thanks for digging up the ref, @SebastianZ! Yes, we discussed this last year; the reasoning is to give all the mixing functions a consistent grammar form so they can all benefit from all the mixing features, even if they have a legacy grammar that looks a little different.

[svgeesus]

Thanks, @SebastianZ and @tabatkins

So, are any browsers implementing this, or expressing interest?

[tabatkins]

At the moment, all of the mix functions are not yet implemented. But the mix functions in general have implementor interest; we needed them to solve font palette mixing, for example.

[cdoublev]

The "new" variant has an optional <color-interpolation-method>, while omitting in in the original syntax is still discussed in #10484 , but I do not see the people involved in the new variant taking part in that discussion, so: can you please tell me if there is a reason to specifically allow omitting it in the new variant, or do you ultimately want it to match the original variant?

[emilio]

cc #11532 where @LeaVerou proposes removing that mandatory interpolation method