Selects the specified display as the current source display. This
    causes the output of all TYPE and EXAMINE/SOURCE commands to go
    to that display. The display specified must be a source display.

    If you do not specify a display, the current source display is
    unselected and no display has the source attribute.

    By default, for all languages except MACRO-32, the SRC display
    has the source attribute. If the language is set to MACRO-32, no
    display has the source attribute by default.