code: func (c *FSM) applyCoordinateBatchUpdate(buf []byte, index uint64) interface{} {
  	var updates structs.Coordinates
  	if err := structs.Decode(buf, &updates); err != nil {
  		panic(fmt.Errorf("failed to decode batch updates: %v", err))
  	}
  	defer metrics.MeasureSince([]string{"fsm", "coordinate", "batch-update"}, time.Now())
  	if err := c.state.CoordinateBatchUpdate(index, updates); err != nil {
  		return err
  	}
  	return nil
  }
docs: // applyCoordinateBatchUpdate processes a batch of coordinate updates and applies
  // them in a single underlying transaction. This interface isn't 1:1 with the outer
  // update interface that the coordinate endpoint exposes, so we made it single
  // purpose and avoided the opcode convention.