anchor.diff:  ;
   // R722
   expr : 
  -  (   expr definedBinaryOp   )?   level5Expr
  +  level5Expr ( definedBinaryOp   expr )?
   ;
   // R721
   equivOp : 
  
positive.code: ;
  // R710
  level3Expr : 
    (   level3Expr concatOp   )?   level2Expr
  ;
  // R711
  concatOp : 
  
negative.code: variable
  ;
  // R914
  fformat : 
  defaultCharExpr
  | label
  |  ASTERISK 
  