<?xml version="1.0" encoding="ISO-8859-1" ?>

<ROOT>
 <NAV>
  <LINK>seite01.php</LINK>
  <NAME>Seite 1</NAME>
  <ID>1</ID>
 </NAV>
 <NAV>
  <LINK>seite02.php</LINK>
  <NAME>Seite 2</NAME>
  <ID>3</ID>
 </NAV>
 <NAV>
  <LINK>seite03.php</LINK>
  <NAME>Seite 3</NAME>
  <ID>2</ID>
 </NAV>
</ROOT>

$xml = '<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<root>
<a id="0"></a>
<a id="7"></a>
<a id="5"></a>
<a id="1"></a>
<a id="6"></a>
<a id="4"></a>
<a id="2"></a>
<a id="9"></a>
</root>';

$parser = new DOMDocument();
$parser->loadXML($xml);

$root = $parser->childNodes->item(0);
$nodes = array();

for ($i = 0; $i < $root->childNodes->length; $i++)
{
    $child = $root->childNodes->item($i);
    if ($child->nodeName == 'a')
    {
        $nodes[] = $child;
    }
}

for ($i = count($nodes) - 1; $i >= 1; $i--)
{
    for ($j = 1; $j < $i; $j++)
    {
        if ($nodes[$j]->attributes->getNamedItem('id')->nodeValue >
                $nodes[$j + 1]->attributes->getNamedItem('id')->nodeValue)
        {
            $temp = $nodes[$j];
            $nodes[$j] = $nodes[$j + 1];
            $nodes[$j + 1] = $temp;
        }
    }
}

foreach ($nodes as $node)
{
    echo $node->attributes->getNamedItem('id')->nodeValue;
}

<a id="0">Link 1</a>

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE gruss SYSTEM "gruss.dtd">
<?xml-stylesheet type="text/xsl" href="sortSheet.xsl" ?>
<data>
	<value>2</value>
	<value>4</value>
	<value>1</value>
	<value>3</value>
	<value>5</value>
</data>

<?xml version="1.0" encoding="iso-8859-1"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="/">
 <data>
  <xsl:for-each select="data/value">
  	<xsl:sort select="."/>
  	<value><xsl:value-of select="."/></value>
  </xsl:for-each>
 </data>
</xsl:template>

</xsl:stylesheet>