We will begin by making use of the WDDX functions that PHP offers for free, no need to create our own XML parser or even know the WDDX DTD, we can just use them and be happy.

The WDDX functions do not need any external library, and implement methods to generate, serialize and deserialize information into WDDX packets.

WDDX, the Web Distributed Data Exchange, is an XML application that:

"... is a mechanism for exchanging complex data structures between application environments. It has been designed with web applications in mind. WDDX consists of a language and platform neutral representation of instantiated data based on XML 1.0 (which is defined using this DTD) and a set of serializer/ deserializer components for every environment that uses WDDX. The process of creating an XML representation of application data is called serialization. The process of instantiating application data from a WDDX XML representation is called deserialization. "

(Quoted from: "WDDX Document Type Definition (DTD)", http://www.wddx.org/DTD.htm)

WDDX has a simple DTD, and can be used to serialize variables of different types. The DTD recognizes variables of type string, numeric, and boolean, as well as arrays (when the indexes are numeric) and structures (when the indexes are strings, also called associative arrays). Complex data structures can also be represented (e.g. arrays of arrays).