This message occurs when an application requests a message by issuing a WinPeekMsg or a WinGetMsg function.
If the message that is to be retrieved represents a pointer related event, this message is sent to a window to determine whether the message is in fact destined for that window.
This message is only sent if the window class has the CS_HITTEST style set.
Note: The handling of this message determines whether a disabled window can process pointing device events.