anchor.diff:      : IDENTIFIER
       | bracketedExpr
       ;
  -    
  +
   bracketedExpr
       : OPEN_PAREN! orExpr CLOSE_PAREN!
       ;
  
positive.code: orExpr
      : andExpr ( "or"^ andExpr )*
      ;
      
  andExpr
      : atom ( "and"^ atom )*
      ;
  
negative.code: //
  // Grammar for path expressions
  //
  
  header {
  