The action taken by the default dialog procedure is such that the values passed in mp1 and mp2, and the values returned in mresReply are defined for each msg.

The default dialog procedure provides default processing for any dialog window messages that an application chooses not to process. It can be used to ensure that every message is processed and is called with the same parameters that were received by the dialog procedure.

The action of the WinDefDlgProc function on receiving messages is precisely the same as for the frame window procedure except for WM_CLOSE messages where WinDismissDlg will be called. If an application processes a message instead of sending it to the WinDefDlgProc function, it may be required to perform some or all of the frame window procedure actions for itself.