[mediaqueries-5] Type checking math functions resolving to a feature dimension value

[cdoublev]

A feature dimension value specified with a math function matches <dimension> in <mf-value>:

<mf-value> = <number> | <dimension> | <ident> | <ratio>

According to CSS V&U, a math function can only resolve to a subset of <dimension>:

A math function resolves to <number>, <length>, <angle>, <time>, <frequency>, <resolution>, <flex>, or <percentage> according to which of those productions its type matches.

So implementations should either expand <dimension> to this restricted set when it is produced by <mf-value>, or they should skip type checking a math function matching <mf-value>, since <mf-value> must be validated against the grammar of the specified feature value anyway.

This can be clarified or, <calc-sum> could be produced instead of <number> | <dimension> | <ratio>, which would be on par with *-progress(<mf-name>, <calc-sum>, <calc-sum>), which requires validating <calc-sum> according to the grammar of the specified <mf-name> (or only its numeric type? #10802).

This would mean that queries like @media (10vw + 1rem < width) {} or @media ((10vw + 1rem) < width) {} would work.

[tabatkins]

So implementations should either expand to this restricted set when it is produced by , or they should skip type checking a math function matching , since must be validated against the grammar of the specified feature value anyway.

I don't understand what you're asking for here. A math function resolves to one of those types. Those types match <number> or <dimension>, which is what <mf-value> requires. So a valid math function (per its normal validity rules) is always a valid <mf-value>.

[cdoublev]

Right, sorry, <dimension> does not expand to these types. Each of these is a <dimension>.

My point is that for an input calc(1px) < width, a CSS parser processing the grammar would first see <number> and fail to get a match, then try to replace it with a math function but fail to match its numeric type, then see <dimension> and fail to get a match and is not allowed to replace it with a math function.