Description:
------------
DomDocumentFragments witch replaced existing Nodes in a DomDocument is not globaly useable.

 * Create a DocumentFragment on an existing DomDocument.
 * Append one (or more) Child to this Fragment
 * Replace existing Node with this Fragment

The Methods DomDocument->saveXML() displays the Document in the right way. 
When you use getElementsByTagName, XPath, or e.g. the XSL Extension these new Elements are not there.

So in the Example the <replacement> will never be useable, only viewable.

Reproduce code:
---------------
<?php
$xmlData = <<<XMLCONTENT
<?xml version="1.0" encoding="utf-8"?>
<test>
    <replace />
</test>
XMLCONTENT;

$dom = new DomDocument;
$dom->loadXML( $xmlData );

$fragment = $dom->createDocumentFragment();
$replacement = $dom->createElement( 'replacement' );
$fragment->appendChild( $replacement );
$additionalNode = $dom->createElement( 'additionalNode' );
$fragment->appendChild( $additionalNode );

foreach( $dom->getElementsByTagName( 'replace' ) AS $node ) {
    $node->parentNode->replaceChild( $fragment, $node );
}

echo "replacement tags found: " . $dom->getElementsByTagName( 'replacment' )->length . "\n\n";
echo "xml code used:\n";
echo $dom->saveXML();
?>

Expected result:
----------------
replacement tags found: 0

xml code used:
<?xml version="1.0" encoding="utf-8"?>
<test>
    <replacement/><additionalNode/>
</test>

Actual result:
--------------
replacement tags found: 1

xml code used:
<?xml version="1.0" encoding="utf-8"?>
<test>
    <replacement/><additionalNode/>
</test>