The example given in the XEmacs user's manual does not work correctly. The following sequence of keystrokes gives incorrect results (this can be done in the *scratch* buffer): 1. M-x abbrev-mode 2. type the word construction, M-x a g to add the abbreviation `cnst' for it 3. type c n s t SPACE -- everything goes as planned 3. type r e M-' (abbrev-prefix-mark) c n s t SPACE -- nothing happens This example was taken from the section "Controlling Abbrev Expansion". The example works correctly in GNU Emacs. It does not work for me in 20.4,