Concepts

Principially the same as in Java, there are:

tree-oriented interfaces

DOM full repertoire of operations (read, validate, write incl. prettyprinting, programmatic creation of docs, elements, etc.)

stream-based (pull)

SimpleXML - since PHP 5.0 part of the core PHP, very simple and frequently used interface, enables direct iteration (traversal) through XML elements, direct evaluation of XPath expressions etc.

Also see SimpleXML (PHP) at W3Schools

event-driven

SAX - similarly as in Java, in all recent PHP compilations