I implemented the appendXML($xmlfragment) method in the DomDocumentFragment class of the DOM extension in PHP 5.
This method allows easy and fast adding of XML DocumentFragment strings. While it was somehow possible to do that with the current methods, it was not really satisfying. Unfortunately this new method won't make it into PHP 5.0.0, because of the feature freeze and very near stable releasse.
More about the new method, how to use it (and how the same is done in nowadays PHP 5.0.0) can be found in my little article on our Wiki.