XML_Serializer serializes complex data structures like arrays or object as XML documents. This class helps you generating any XML document you require without the need for DOM.
Currently there are two ways in which XML_Serializer can be used in your applications:
use XML_Serializer's functionality to create XML documents in a specific XML application (e.g. RDF) that is being processed by an existing script)
use XML_Serializer's functionality to serialize data structures that have to be unserialized at a later point. This is possible by adding type information to all XML elements.
The package not only contains a serializer class but also a matching XML_Unserializer, which is able to virtually read any XML document and return an array or object structure that represents the data stored in the document.
There are several tutorials on XML_Serializer available, that help you get started.
Instant XML with PHP and PEAR::XML_Serializer by Harry Fuecks
Serializing XML With PHP by Vikram Vaswani