WDDX is an open technology proposed by Allaire Corporation; it's an XML vocabulary for describing basic and complex data structures such as strings, arrays, and recordsets in a generic fashion, so that they can be moved between different web scripting platforms using only HTTP. PHP supports WDDX, and so do most other prominent web scripting languages (for example, Perl, ASP, and Cold Fusion). You can learn more about WDDX at http://www.openwddx.org/. These functions transform PHP variables into WDDX packets and back. To use them, you must compile PHP with XML support.