Hallo
In der
msdn findest du Infos zu den Hook Typen.
Bemerkungen zu
WM_APPCOMMAND Notification
Zitat:
If a child window does not process this message and instead calls DefWindowProc, DefWindowProc will send the message to its parent window. If a top level window does not process this message and instead calls DefWindowProc, DefWindowProc will call a shell hook with the hook code equal to HSHELL_APPCOMMAND.