[css-values-5] How to determine the type of <progress> in calc-mix()?

[cdoublev]

The type of calc-mix() must be made consistent with the type of its <progress>, which is defined with:

<progress> = [<percentage> | <number> | <'animation-timeline'>] && [by <easing-function>]?

What is the type of <progress> in these examples?

1. calc-mix(0%, 1px, 2px) in a <length-percentage> context
2. calc-mix(calc(0%), 1px, 2px) in a <length-percentage> context
3. calc-mix(--timeline, 1px, 2px)

My respective guesses:

1. [percentage → 1]
2. [percentage → 1]
3. []

In my opinion, the type of calc(0%) matching <progress> should always be [percentage → 1], whatever the "higher" context is.

[cdoublev]

Sorry, I missed that <percentage> should actually have been replaced with <percentage-token> in the <progress> production rule, as explained in the detailed definition appearing below the production rule:

<percentage-token> [...]

Note: This only allows literal percentages, like 15%; calculations like calc(100% / 7) will not work [...].

But this restriction seems to be motivated solely by internal constraints that authors would not understand it, imo.

Would it not be possible to say that <percentage> always resolves to [percentage → 1] as a term of a math function replacing <progress>?