Library /sys$common/syshlp/pca$help.hlb SELECT, Qualifiers, /OUTPUT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    If you specify a display, selects it as the current output
    display. This causes PCA output that is not already directed
    to another display to go to that display. The display specified
    must be either an output display or the PROMPT display.

    If you do not specify a display, the PROMPT display is selected
    as the current output display. By default, the OUT display has
    the output attribute.