VZAA, chapter 24 (Interfaces with other  languages),  page
  405

     The validity constraint on actual  arguments  of  the
     Address  form  is  clause  4 of the argument validity
     rule, which makes $` f' valid as actual argument to a
     call  if  and  only  if  `f'  is  the final name of a
     feature of the enclosing class, and that  feature  is
     not a constant attribute (which has no address).