Why does @codemirror/selection use a separate layer?

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I’m mostly just curious, why does the selection extension use an underlay instead of using decoration marks?

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Depending on the answer, I’m also wondering if it’s worth considering having a layer abstraction that sort of mimic how decorations work but they use a separate layer instead of modifying the content dom, selections can be built on top of this. Obviously this can be created as a standalone package like the tooltip package.

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Because the selection doesn’t just cover the text, but forms a rectangle all the way to the end of selected lines, and avoids gaps between lines and such.

This could probably be abstracted in a way that allows custom backdrop layers, yes, if a convincing use case is found. Would be hard not to obscure or be obscured by the selection though.

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