fltk::Output | +----fltk::MultilineOutput
#include <fltk/MultilineOutput.h>
Long lines of text will have to be horizontally scrolled, currently the only way to do this is to drag the mouse or move the cursor. You may want fltk::WordwrapOutput instead.
Because there are no scrollbars, this is probably only good for small bits of text, 10 lines at most. More powerful editing is available from the fltk::TextEditor widget.