Why aren't events masked by the last several frames generated by the rendering system? If a page is divided into two columns with the left half originating fro

Why aren't events masked by the last several frames generated by the rendering system? If a page is divided into two columns with the left half originating from the source origin and the right half from a delegated origin, why should the source origin observe interaction events from the right half, or vice versa? We should be able to press a hotkey and immediately see at-a-glance who is operating what.