public function unregister($alias, $remove_instances=false)
	{
		$alias = strtolower($alias);

		if ($remove_instances && array_key_exists($alias, $this->instances))
		{
			$this->instances[$alias] = null;
			unset($this->instances[$alias]);
		}

		unset($this->services[$alias]);

		return $this;
	}