character is only partially visible, nil is returned, unless the
optional argument PARTIALLY is non-nil. If POS is only out of view
because of horizontal scrolling, return non-nil. If POS is t, it
-specifies the position of either the first position displayed on the
-last visible screen line in WINDOW, or the end-of-buffer position,
-whichever comes first. POS defaults to point in WINDOW; WINDOW defaults
-to the selected window.
+specifies either the first position displayed on the last visible
+screen line in WINDOW, or the end-of-buffer position, whichever comes
+first. POS defaults to point in WINDOW; WINDOW defaults to the
+selected window.
If POS is visible, return t if PARTIALLY is nil; if PARTIALLY is non-nil,
the return value is a list of 2 or 6 elements (X Y [RTOP RBOT ROWH VPOS]),