The text passed to a display pane can be provided either as a single string containing newlines, or else as a list of strings where each string represents a line.
There are several classes which can display text, as follows:
Displays a single line of text.
(capi:contain (make-instance
'capi:display-pane
:text
'("One" "Line" "At" "A" "Time...")))
(setq dp (capi:contain
(make-instance
'capi:display-pane
:text
'("One" "Line" "At" "A" "Time...")
:visible-min-height
'(:character 5))))
(capi:apply-in-pane-process
dp #'(setf capi:display-pane-text)
'("Some" "New" "Text") dp)
CAPI Reference Manual - 15 Dec 2011