protected static function build_list($type = 'ul', array $list = array(), $attr = false, $indent = '')
	{
		if ( ! is_array($list))
		{
			$result = false;
		}

		$out = '';
		foreach ($list as $key => $val)
		{
			if ( ! is_array($val))
			{
				$out .= $indent."\t".html_tag('li', false, $val).PHP_EOL;
			}
			else
			{
				$out .= $indent."\t".html_tag('li', false, $key.PHP_EOL.static::build_list($type, $val, '', $indent."\t\t").$indent."\t").PHP_EOL;
			}
		}
		$result = $indent.html_tag($type, $attr, PHP_EOL.$out.$indent).PHP_EOL;
		return $result;
	}