In the following sample, please place the mouse pointer over the button and try to close the dialog using ALT-F4. It will not close.
EMG
#include "Fivewin.ch"
FUNCTION MAIN()
LOCAL oDlg
DEFINE DIALOG oDlg
@ 1, 1 BTNBMP;
FILE "C:\FWH\BITMAPS\OPEN.BMP";
NOBORDER
ACTIVATE DIALOG oDlg;
CENTER
RETURN NILEMG