-@defun pos-visible-in-window-p &optional position window
-This function returns @code{t} if @var{position} is within the range
-of text currently visible on the screen in @var{window}. It returns
-@code{nil} if @var{position} is scrolled vertically out of view. The
-argument @var{position} defaults to the current position of point;
-@var{window}, to the selected window. Here is an example:
+@defun pos-visible-in-window-p &optional position window partially
+This function returns non-@code{nil} if @var{position} is within the
+range of text currently visible on the screen in @var{window}. It
+returns @code{nil} if @var{position} is scrolled vertically out of
+view. Locations that are partially obscured are not considered
+visible unless @var{partially} is non-@code{nil}. The argument
+@var{position} defaults to the current position of point in
+@var{window}; @var{window}, to the selected window.
+
+The @code{pos-visible-in-window-p} function considers only vertical
+scrolling. If @var{position} is out of view only because @var{window}
+has been scrolled horizontally, @code{pos-visible-in-window-p} returns
+non-@code{nil} anyway. @xref{Horizontal Scrolling}.
+
+If @var{position} is visible, @code{pos-visible-in-window-p} returns
+@code{t} if @var{partially} is @code{nil}; if @var{partially} is
+non-@code{nil}, it returns a list of the form @code{(@var{x} @var{y}
+@var{partial})}, where @var{x} and @var{y} are the pixel coordinates
+relative to the top left corner of the window, and @var{partial} is
+@code{nil} if the character after @var{position} is fully visible;
+otherwise it is a cons @code{(@var{rtop} . @var{rbot})} where the
+@var{rtop} and @var{rbot} specify the number of invisible pixels at
+the top and bottom of the row at @var{position}.
+
+Here is an example: