public function find($criteria)
	{
		if (!$criteria)
		{
			error_log("collection error: no criteria specified");
			return null;
		}

		else if (is_callable($criteria))
		{
			foreach ($this->models as $model)
				if ($criteria($model)) return $model;
		}
		else if (is_a($criteria, "SnooPHP\Model\Model"))
		{
			foreach ($this->models as $i => $model)
				if ($model == $criteria) return $i;
		}

		return null;
	}