private function updateTrailing($pos = 'lft', $base = 0, $add = true)
	{
		// Reposition new values of displaced items
		$query = $this->getQuery();

		$query->update($this->getTableName());
		$query->set([
			$pos => new Value\Raw($pos . ($add ? '+' : '-') . '2'),
		]);
		$query->where($pos, '>=', $base)
		      ->where('id', '!=', $this->id)
		      ->execute();

		return $this;
	}