Duplicates all drawing operations onto multiple child targets, thus
producing identical output on multiple visuals.
OPTIONS
The argument to display-multi is a colon- (:) separated list of
target specs to draw on. Because target specs can (and often do)
contain colons, they need to be enclosed in parentheses.
target-spec
Specifies the target which to draw on (the parent target). This
defaults to automatic selection (just like using
ggiOpen(NULL) when GGI_DISPLAY is not set).
