The parent window for the richedit control on creation is the one that
receives notify messages, even after the parent has been changed using
SetParent.
- A HWND can be safely marshaled over a LONG as its payload is not
a pointer but a user handle.
- Use GetWindowLongPtr instead of GetWindowLong to retrieve a pointer.
Certain operations will simply not be done for windowless richedit
controls, such as WM_PAINT which isn't done for windowless richedit
controls since ITextServices provides a TxDraw method.