1.DBG> SHOW EDITOR
      The editor is SPAWNed, with command line
          "EDT/START_POSITION=(n,1)"
      DBG>

      In this example, the EDIT command spawns the EDT editor in
      a subprocess. The /START_POSITION qualifier appended to the
      command line indicates that the editing cursor is initially
      positioned at the beginning of the line that is centered in the
      debugger's current source display.

    2.DBG> SET EDITOR/CALLABLE_TPU
      DBG> SHOW EDITOR
      The editor is CALLABLE_TPU, with command line "TPU"
      DBG>

      In this example, the SHOW EDITOR command indicates that the
      EDIT command invokes the callable version of the DEC Text
      Processing Utility (DECTPU). The editing cursor is initially
      positioned at the beginning of source line 1.