PHP 5 has a completely new set of XML extensions that address major problems in PHP 4's XML extensions. While PHP 4 allows you to manipulate XML, its XML tools are only superficially related. Each tool covers one part of the XML experience, but they weren't designed to work together, and PHP 4 support for the more advanced XML features is often patchy. Not so in PHP 5. The new XML extensions:
Work together as a unified whole
Are standardized on a single XML library: libxml2
Fully comply with W3 specifications
Efficiently process data
Provide you with the right XML tool for your job
Additionally, following the PHP tenet that creating web applications should be easy, there's a new XML extension that makes it simple to read and alter XML documents. The aptly named SimpleXML extension allows you to interact with the information in an XML document as though these pieces of information are arrays and objects, iterating through them with foreach loops and editing them in place merely by assigning new values to variables.