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[css2?] Hit testing / z-ordering of the root element vs the body. #11744

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emilio opened this issue Feb 19, 2025 · 0 comments
Open

[css2?] Hit testing / z-ordering of the root element vs the body. #11744

emilio opened this issue Feb 19, 2025 · 0 comments
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@emilio
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emilio commented Feb 19, 2025

Consider this reduced test-case for Mozilla bug 1948937:

<!DOCTYPE html>
<style>
  html, body {
    position: relative;
  }

  body {
    z-index: -2;
  }
</style>
<input type="text">

In Firefox, you can't hit the <input type=text>, because it's ordered under the <html> box. In Blink and WebKit you can.

If you make the same test-case with two other elements, then Blink and WebKit agree with Gecko, as expected.

So I think the behavior in WebKit/Blink probably is a consequence of the background propagation to the viewport, but I still think this probably shouldn't work? I guess whether it works depends on whether you consider the box hit-testable, or the background area... If so, I should probably file WebKit and Blink issues, but since the spec for hit testing doesn't exist, I kinda want to confirm my intuition is correct.

This is probably changeable on Gecko's end if needed, but Gecko's behavior seems more consistent to me...

cc @bfgeek @dbaron @smfr @tabatkins
@emilio emilio added the CSS2 label Feb 19, 2025
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