The command @kbd{M-x compare-windows} compares the text in the
current window with that in the window that was the selected window
before you selected the current one. (For more information about
-windows in Emacs, @ref{Windows}.) Comparison starts at point in each
-window, after pushing each initial point value on the mark ring
+windows in Emacs, @pxref{Windows}.) Comparison starts at point in
+each window, after pushing each initial point value on the mark ring
(@pxref{Mark Ring}) in its respective buffer. Then it moves point
forward in each window, one character at a time, until it reaches
characters that don't match. Then the command exits.