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