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[css-mixins-1] Do arbitrary function substitution before evaluation #11449

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Jan 14, 2025
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[css-mixins-1] Do arbitrary function substitution before evaluation #11449

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20 changes: 9 additions & 11 deletions css-mixins-1/Overview.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -228,13 +228,6 @@ At computed-value time,
every <<dashed-function>> must be [=substitute a dashed function|substituted=]
before finally being checked against the property's grammar.

When a value is being computed,
substitution of ''var()'', ''env()'' and ''attr()''
must take place <em>before</em> <<dashed-function>> substitution.

Note: This means arguments passed to a custom function
never contain ''var()'', or similar functions.

A ''var()'' function within a [=local variable=],
or within the ''@function/result'' descriptor,
invokes [=locally substitute a var()|local substitution=],
Expand All @@ -260,10 +253,13 @@ described in [[!css-variables]].
* Append the result of [=resolving an argument=] to |dependency values|,
using |dependency value| as value,
and |dependency| as parameter.
4. [=Evaluate a custom function=],
4. [=substitute arbitrary substitution functions|Substitute=]
any [=arbitrary substitution functions=]
within |dashed function|'s arguments.
5. [=Evaluate a custom function=],
using |function|, |dashed function| and |dependency values|.
5. If failure was returned, return failure.
6. Otherwise,
6. If failure was returned, return failure.
7. Otherwise,
replace the <<dashed-function>> with the [=equivalent token sequence=]
of the value resulting from the evaluation.
</div>
Expand Down Expand Up @@ -402,8 +398,10 @@ Parameters and Locals {#parameters}
A <dfn>resolved local value</dfn> is the value of a [=local variable=] or [=descriptor=], except:

* Any ''var()'' functions are replaced by [=locally substitute a var()|local substitution=].
* Any ''env()'' or ''attr()'' functions are substituted normally.
* Any <<dashed-function>>s are replaced by [=substitute a dashed function|dashed function substitution=].
* Any [=arbitrary substitution functions=]
other than ''var()'' and <<dashed-function>>s
are substituted normally.

If any substitution algorithm returns failure,
then the [=resolved local value=] of a [=local variable=]
Expand Down