anchor.diff:  IDENTIFIER
       :  ('a'..'z'|'_') ('a'..'z'|'_'|'0'..'9')*
       ;
  -    
  +
  
positive.code: //
  // Grammer for path expressions
  //
  
  header {
  
negative.code:     : IDENTIFIER
      | bracketedExpr
      ;
  
  bracketedExpr
      : OPEN_PAREN! orExpr CLOSE_PAREN!
      ;
  