Explain "&" in the syntax tableaux

Us SGML old-timers and RELAX NG grammarians all know what it means, but...

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | The belief in a supernatural source of
http://nwalsh.com/            | evil is not necessary; men alone are
                              | quite capable of every
                              | wickedness.--Joseph Conrad