try_scrolling question

[Po Lu]

What does the "value" in the comment on top of `try_scrolling' refer to?

   Try scrolling PT into view in window WINDOW.  JUST_THIS_ONE_P means
   only WINDOW is redisplayed in redisplay_internal.  TEMP_SCROLL_STEP
   has the same meaning as emacs_scroll_step, and is used in
   redisplay_window to bring a partially visible line into view in the
   case that only the cursor has moved.

   LAST_LINE_MISFIT should be true if we're scrolling because the last
   screen line's vertical height extends past the end of the screen.

   Value is
   ^^^^^

   1    if scrolling succeeded

   0    if scrolling didn't find point.

   -1 if new fonts have been loaded so that we must interrupt redisplay,
   adjust glyph matrices, and try again.

Does it mean the return value of try_scrolling?  If so, I don't
understand how 0 (SCROLLING_SUCCESS) is returned if it can't find point,
and how -1 can be returned at all.

Am I missing something here?

Thanks.