Adding a block of XML as child of a SimpleXMLElement object

I have this SimpleXMLElement object with a XML setup similar to the following...

$xml = <<<EOX
<books>
    <book>
        <name>ABCD</name>
    </book>
</books>
EOX;

$sx = new SimpleXMLElement( $xml );

Now I have a class named Book that contains info. about each book. The same class can also spit out the book info. in XML format akin the the above (the nested block).. example,

$book = new Book( 'EFGH' );
$book->genXML();

... will generate
<book>
    <name>EFGH</name>
</book>

Now I'm trying to figure out a way by which I can use this generated XML block and append as a child of so that now it looks like... for example..

// Non-existent member method. For illustration purposes only.
$sx->addXMLChild( $book->genXML() );    

...XML tree now looks like:
<books>
    <book>
        <name>ABCD</name>
    </book>
    <book>
        <name>EFGH</name>
    </book>
</books>

From what documentation I have read on SimpleXMLElement, addChild() won't get this done for you as it doesn't support XML data as tag value.

Solution

Two solutions. First, you do it with the help of libxml / DOMDocument / SimpleXML: you have to import your $sx object to DOM, create a DOMDocumentFragment and use DOMDocumentFragment::appendXML():

$doc = dom_import_simplexml($sx)->ownerDocument;

$fragment = $doc->createDocumentFragment();     
$fragment->appendXML($book->genXML());
$doc->documentElement->appendChild($fragment);

// your original $sx is now already modified.

See the Online Demo.

You can also extend from SimpleXMLElement and add a method that is providing this. Using this specialized object then would allow you to create the following easily:

$sx = new MySimpleXMLElement($xml);

$sx->addXML($book->genXML());

Another solution is to use an XML library that already has this feature built-in like SimpleDOM. You grab SimpleDOM and you use insertXML(), which works like the addXMLChild() method you were describing.

include 'SimpleDOM.php';

$books = simpledom_load_string(
    '<books>
        <book>
            <name>ABCD</name>
        </book>
    </books>'
);

$books->insertXML(
    '<book>
        <name>EFGH</name>
    </book>'
);