Make mouse event targets agnostic to mousedown event cancellation when the pointer is dragged out of an iframe. When the mouse is dragged out of an iframe, all browsers (including Chrome) send mousemove and mouseup events to the iframe. However, if the mousedown event is cancelled, Chrome today maintains an old WebKit exception that mousemove and mouseup events are sent to the outer frame. WebKit removed this exception last year, and Mozilla never showed this behavior in recent years. This feature will remove the Chrome-only exception for this special case.
Samples: https://mustaqahmed.github.io/web/interop/cancel-mousedown-in-iframe-top.html https://codepen.io/mustaqahmed/full/yLjBraJ