The DOM XML extension has been overhauled in PHP 4.3.0 to better comply with the DOM standard. The extension still contains many old functions, but they should no longer be used. In particular, functions that are not object-oriented should be avoided.
The extension allows you to operate on an XML document with the DOM API. It also provides a function domxml_xmltree() to turn the complete XML document into a tree of PHP objects. Currently, this tree should be considered read-only - you can modify it, but this would not make any sense since DomDocument_dump_mem() cannot be applied to it. Therefore, if you want to read an XML file and write a modified version, use DomDocument_create_element(), DomDocument_create_text_node(), set_attribute(), etc. and finally the DomDocument_dump_mem() function.
This extension has been moved to the » PECL repository and is no longer bundled with PHP as of PHP 5.0.0.