The following MSceneMessage methods differ from their C++ counterparts.
| msg, func, clientData=None, status=None) |
bool. You may also return nothing
at all which actually returns the value None which is interpreted
as False. So similar to the C++ version you can either register
a callback that does not return any value or that returns a boolean.
However, in both cases the wrapper uses the same C++ version of
addCallback().