Re: [csswg-drafts] [css-values] Spec does not reject duplicate `<request-url-modifier>`s, but WPT does (#12151)

Given there is enough discussion here, I want to simplify the prosed resolution to just the content for this issue. So, here it is again, but without the unknown modifiers bit.

I'm not convinced allowing duplicate modifiers makes sense and that these modifiers fall into the same class as the ones @cdoublev mentions "representing resources, instructions, function arguments, etc". 

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Updated resolution:

Update grammar for `<url>` to disallow duplicate `<request-url-modifier>` productions by changing the grammar from:

```
<url> = <url()> | <src()>

<url()> = url( <string> <url-modifier>* ) | <url-token>
<src()> = src( <string> <url-modifier>* )
```

to

```
<url> = <url()> | <src()>

<url()> = url( <string> <url-modifiers>? ) | <url-token>
<src()> = src( <string> <url-modifiers>? )
```

and adding the definition of `<url-modifiers>` as:

 ```
<url-modifiers> = <request-url-modifier>
<request-url-modifier> = <crossorigin-modifier> || <integrity-modifier> || <referrerpolicy-modifier>
<crossorigin-modifier> = crossorigin(anonymous | use-credentials)
<integrity-modifier> = integrity(<string>)
<referrerpolicy-modifier> = referrerpolicy(no-referrer | no-referrer-when-downgrade | same-origin | origin | strict-origin | origin-when-cross-origin | strict-origin-when-cross-origin | unsafe-url)
```

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Received on Thursday, 26 June 2025 16:06:20 UTC