php simple xml get inner xml

$s = <<<STR
<?xml version="1.0" encoding="UTF-8"?>
<store>
  <owner name="huypv"></owner>
  <book id="b#ffdg01">
    <page i="12">
    <content>
    <![CDATA[ Taj vj sao laj th3?! ]]>
    </content>
    </page>
  </book>
 
  <book id="b#ffdg02">
    <page i="13">
    <content>
    <![CDATA[ Taj vj sao laj th3 v2.0?! ]]>
    </content>
    </page>
  </book>
 
  <extra>
    <year>2012</year>
    <gold>true</gold>
    <silver>60%</silver>
  </extra>
 
</store>
STR;
function getInnerXML($xml) {
  $innerXML = '';
  foreach (dom_import_simplexml($xml)->childNodes as $child) {
    $innerXML .= $child->ownerDocument->saveXML($child);
  }
  return $innerXML;
}

$xml = simplexml_load_string($s);
# get Taj vj sao laj th3 v2.0?!
echo (string)$xml->book[1]->page->content;

# get 60%
echo $xml->extra[0]->silver;

# get huypv
$a = $xml->owner->attributes();
var_dump((string)$a['name']);

# get innerXML book-0
var_dump(getInnerXML($xml->book[0]));

var_dump($xml->book[0]->asXML());