In fact, Chrome 76 (released in 2019) and newer versions seem to all match our rendering of testcase 1. Chrome 75 and earlier matches Safari 15.1. Without having dug into the relevant specs/code, I don't know for absolute sure who's correct. But given that Chrome is the only browser engine that's been observed to have changed behavior here, it feels reasonable to suspect that their newer behavior (which matches our behavior) is correct. And at a minimum, this doesn't present as much of a webcompat issue for us, now that we're not on our own. Given that I'm the reporter, I'm not going to feel too bad about closing this as INVALID, in the sense that our behavior is now probably-correct (and/or required for compatibility, given that the dominant rendering engine matches us on this now). I think the webcompat reports that have been linked here in recent years (since Chrome 76) are likely to in fact be cases where sites are depending on https://bugs.chromium.org/p/chromium/issues/detail?id=1141209 , which is also about floats and negative margins. The relevant difference is: - In this bug here, the testcase has a *float with a negative margin* - in [the chrome bug](https://bugs.chromium.org/p/chromium/issues/detail?id=1141209), the testcase has a float *next to something* with a negative margin (but the float itself is not the thing with the negative margin).
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In fact, Chrome 76 (released in 2019) and newer versions seem to all match our rendering of testcase 1. Chrome 75 and earlier matches Safari 15.1. Without having dug into the relevant specs/code, I don't know for absolute sure who's correct. But given that Chrome is the only browser engine that's been observed to have changed behavior here, it feels reasonable to suspect that their newer behavior (which matches our behavior) is correct. And at a minimum, this doesn't present as much of a webcompat issue for us, now that we're not on our own. Given that I'm the reporter, I'm not going to feel too bad about closing this as INVALID, in the sense that our behavior is now probably-correct (and/or required for compatibility, given that the dominant rendering engine matches us on this now). I think the webcompat reports that have been linked here in recent years (since Chrome 76) are most-likely cases where sites are depending on https://bugs.chromium.org/p/chromium/issues/detail?id=1141209 , which is also about floats and negative margins. The relevant difference is: - In this bug here, the testcase has a *float with a negative margin* - in [the chrome bug](https://bugs.chromium.org/p/chromium/issues/detail?id=1141209), the testcase has a float *next to something* with a negative margin (but the float itself is not the thing with the negative margin).