Test case:
With slime-autodoc and slime-typeout-frame set up: (setq slime-autodoc-use-multiline-p t) M-x slime-ensure-typeout-frame enlarge the frame with the lisp buffer frame to be wider than the typeout frame; move cursor inside some form with large autodoc string (e.g., w-o-t-s);
The autodoc string shows up in the typeout buffer, but with line breaks according to the width of the lisp buffer, IOW, lines are too partly obscured.
Cheers, Michael