It looks like RawWindowHandle, and the individual platform handles, are marked !Send by default due to the pointers they contain. I couldn't find any documentation one way or another on whether this is explicitly intended to be a part of the safety contract for using a RawWindowHandle or not. I assume that there are some use cases where moving a handle between threads is perfectly safe, and others where it is not. Do existing libraries rely on RawWindowHandle not implementing Send for safety? Or would it be fine for it to impl Send?