Re: [csswg-drafts] [css-values] Grammar syntax for defining excluded idents for <custom-ident> productions (#11924)

#11505 also is about context-sensitive productions; it’s been discussed only by @romainmenke and @cdoublev yet. The goal there is not to list exceptions from the production, but to list (additionally) available keywords. It refers to [`<boolean-expr[<type>]>`](https://drafts.csswg.org/css-values-5/#boolean) for inspiration (see #10457).

I guess, one of the examples from there could become:

~~~~ ebnf
<calc-size()> =
 calc-size( <calc-size-basis>, 
            <calc-sum +[ size ] >
          )
~~~~

However, the production to be amended there is actually `<calc-keyword>` two levels deeper, so maybe it should be: `… <calc-sum ~[ <calc-keyword +[size]> ] > …` 😵‍💫, i.e. _`<calc-sum>` **wherein** any (nested) occurrence of `<calc-keyword>` is **amended by** `size` as an alternative value_. (The tilde prefix may be unnecessary.)

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Received on Tuesday, 10 February 2026 15:22:09 UTC