Re: [csswg-drafts] [css-conditional-3] Stylesheet attached to a document isn't a well-defined concept right now. (#10612)

In hindsight, I am pretty sure a style sheet is attached to a document if it is included in `document.styleSheets` or `document.adoptedStyleSheets`, ie. if it is a non-constructed style sheet (`<link>`, `<style>`), or a constructed style sheet included in `document.adoptedStyleSheets`.

```js
const sheet = new CSSStylesheet
sheet.insertRule('@media all {}')
const rule = sheet.cssRules[0]
rule.matches // false (even if it is "associated" to the document)
document.adoptedStyleSheets.push(rule)
rule.matches // true
```

So an *style sheet attached to the document* is a style sheet included in the [*document or shadow root CSS style sheets*](https://drafts.csswg.org/cssom-1/#documentorshadowroot-document-or-shadow-root-css-style-sheets). I do not know what is the difference with the [*final CSS style sheets*](https://drafts.csswg.org/cssom-1/#documentorshadowroot-final-css-style-sheets).

Also tagging @SebastianZ, which said:

  > If it's attached to a document, it is always evaluated against that document, even when accessed from another document. 

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Received on Saturday, 25 October 2025 11:53:19 UTC