anchor.diff:      {
           initSymbolTable(SCOPE_TOP(Symbols), $message::messageName, $message::isExtension);  
       }
  -	:	message_element zero_or_more_message_elements
  +	:	(extensions|reservations)* message_element zero_or_more_message_elements
       {
           if($message::isExtension) {
               defineExtensionEnd(ctx, $message::messageName);
  
positive.code: 	|	message
  	|	enum_def
  	|	flags_def
      |   extensions
      |   reservations
  	;
  
  extensions
  
negative.code:         }
          ;
  
  reservations : (RESERVE integer TO integer_inclusive ITEM_TERMINATOR -> WS[""])
          {
              defineReservedRange(ctx, $integer.text, $integer_inclusive.text);
          }
  