A popup surface is a transient surface with an added pointer
grab.
An existing implicit grab will be changed to owner-events mode,
and the popup grab will continue after the implicit grab ends
(i.e. releasing the mouse button does not cause the popup to
be unmapped).
The popup grab continues until the window is destroyed or a
mouse button is pressed in any other client’s window. A click
in any of the client’s surfaces is reported as normal, however,
clicks in other clients’ surfaces will be discarded and trigger
the callback.
The x and y arguments specify the location of the upper left
corner of the surface relative to the upper left corner of the
parent surface, in surface-local coordinates.
Serialize into the buffered writer. This function returns no errors,
failures in seializing are generally program errors, and triggers
panicking. Read more