Specifies the scope, relative to the call stack, for which source
    code is displayed in a screen-mode source display. If source code
    is not available for display in that scope, the debugger displays
    source code for the next level down the call stack for which it
    is available.

    The %SOURCE_SCOPE symbol is used in the definition of the
    predefined screen-mode source display SRC:

    DBG> DISPLAY SRC AT H1 SOURCE -
    _DBG> (EXAMINE/SOURCE .%SOURCE_SCOPE\%PC)