Re: [csswg-drafts] [css-highlight-api] : support Paint API for background of highlight (#7139)

This is, unfortunately, impossible. The ::highlight pseudos, like other non-tree-abiding pseudos, restrict what properties can be used for styling with them, limiting themselves to a small list whose effects do not accidentally expose the exact node structure created by the pseudo-element.  In other words, if you have some text like `"<em>emphasized</em> text bar"`, and you highlight the text "emphasized", we don't expose whether the pseudo-element acts like it had generated the pseudo-tags *around* or *inside* the `em` element.

The `background-image` property (or any other property that takes an `<image>` value) would allow an author to tell which node structure was used, so we don't allow it. And the Custom Paint API works by having the `paint()` function be a type of `<image>`, so it would have similar issues.

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Received on Monday, 14 March 2022 21:08:16 UTC