The framework calls this member function when the cursor leaves the client area of the window specified in a prior call to TrackMouseEvent.
This method receives the WM_MOUSELEAVE notification, which is described in the Windows SDK.
This member function is called by the framework to allow your application to handle a Windows message. The parameters passed to your function reflect the parameters received by the framework when the message was received. If you call the base-class implementation of this function, that implementation will use the parameters originally passed with the message and not the parameters you supply to the function.
This method is supported in Windows Vista and later.
Additional requirements for this method are described in Build Requirements for Windows Vista Common Controls.