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[css-values] when should values inside mix() be clamped? #8158
Description
CSS Values and Units Level 4 introduces the mix() function. It's not clear to me reading the spec at what point clamping should be applied for this example:
<div style="font-size: 40px; line-height: mix(0.5, 40px, calc(40px - 3em))"></div>The spec has this to say in the Range Checking section for calc():
Parse-time range-checking of values is not performed within math functions, and therefore out-of-range values do not cause the declaration to become invalid. However, the value resulting from an expression must be clamped to the range allowed in the target context.
I'm not sure what "resulting from an expression" means here. I think the above mix() value could resolve to either:
20pxwhere we clamp the output of thecalc()expression and mix between40pxand0px,0pxwhere we only clamp the output of the entiremix()expression and mix between40pxand-80px, clamping the result-20pxto0px
Assuming that "resulting from an expression" refers to any math function then it would clearly be the first result since mix() is not a math function.
This is somewhat related to #8157 where I raised the issue of what would happen when interpolating between the same two values in the context of an animation.
Activity
Loirooriol commentedon Nov 30, 2022
I would say (1).
mix()uses the grammar of the property to interpolate the expressions, e.g.so interpolating a negative length if the property doesn't understand negative lengths kinda seems wrong.
But an
interp()function from #6697 that would basically be syntax sugar forcalc()then would behave as (2).[css-values-4] Clarify that clamping happens to 'top-level calculatio…
tabatkins commentedon Apr 6, 2023
Yes, it's (1) in this case: each of mix()'s arguments are clamped to allowed range of the context (non-negative). By "expression" I really mean "top-level calculation" and should use that term (and linkify it) instead.
Right, if we stayed purely within math functions the clamping wouldn't happen until the end.