INT 2fH 4002H: Notify Foreground Switch

                                                      Compatibility: Win 3.x 
 Expects: AX    4002H
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 Returns: none
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    Info: VM-aware applications can intercept this fn.  The VDD calls it
          when it is switching the application into the foreground.

          Applications which access video memory while in the background
          will be frozen by the VDD (if the screen is in an unsupported
          video modes INT 2fH 4000H).  This fn notifies the VM-aware
          application that it now has access to video memory.

          If the application has not called INT 2fH 4000H (enable VM-
          assisted video save/restore) then the VDD automatically restores
          the screen before calling this fn.

See Also: INT 2fH 40xxH: Virtual Display Driver Functions
          INT 2fH: Multiplex Interrupt
          DOS Functions
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