SimpleXMLのSimpleXMLElement::asXML()をきれいにインデントする関数

<?php
/**
 * SimpleXMLのasXML()をきれいにインデントする関数
 * @package    Sites
 * @author     Suin <suinyeze@gmail.com>
 * @copyright  2011 Suin
 * @license    MIT License
 */
$xml = '<?xml version="1.0"?><root><foo>FOO</foo><bar /><baz><hoge>HOGE</hoge><fuga /><!-- Comment --><piyo><![CDATA[CDATA desuyo!]]></piyo></baz><!-- Comment --></root>';

echo cleanUpXML($xml);

function cleanUpXML($string)
{
    $string = preg_replace("/>\s*</", ">\n<", $string);
    $lines  = explode("\n", $string);
    $string = '';
    $indent = 0;

    foreach ( $lines as $line )
    {
        $increment = false;
        $decrement = false;

        if ( preg_match('#<\?xml.+\?>#', $line) == true )
        {
            // <?xml … 
        }
        elseif ( preg_match('#<[^/].+>.*</.+>#', $line) == true )
        {
            // Open Tag & Close Tag
        }
        elseif ( preg_match('#<.+/>#', $line) == true )
        {
            // Self-closing Tag
        }
        elseif ( preg_match('#<!.*>#', $line) == true )
        {
            // Comments and CDATA
        }
        elseif ( preg_match('#<[^/].+>#', $line) == true )
        {
            // Open Tag
            $increment = true;
        }
        elseif ( preg_match('#</.+>#', $line) == true )
        {
            // Close Tag
            $decrement = true;
        }
        else
        {
            // Others
        }

        if ( $decrement === true )
        {
            $indent -= 1;
        }

        $string .= str_repeat("\t", $indent).$line."\n";

        if ( $increment === true )
        {
            $indent += 1;
        }
    }

    return $string;
}

<?xml version="1.0"?>
<root>
    <foo>FOO</foo>
    <bar />
    <baz>
        <hoge>HOGE</hoge>
        <fuga />
        <!-- Comment -->
        <piyo>
            <![CDATA[CDATA desuyo!]]>
        </piyo>
    </baz>
    <!-- Comment -->
</root>