Justin Silverton has posted this brief overview of the patTemplate system - what it is and how it can be used in your site.

patTemplate is a set of classes that allow you to separate your php code from design/output, making your code easier to maintain. To identify a certain part of the page as a template, patTemplate uses XML tags to assign a template a unique name and a various attributes (see patTemplate Tags and attributes for a list of all tags and attributes). When parsing a template, the parser divides the page in several chunks and treats them as separate templates. By using patTemplate's API you can hide, display or repeat a certain template.

He describes the different template types (OddEven, Condition, SimpleCondition) and how to use variables inside the templates. He wraps it up with a quick installation overview, both using PEAR and the manual installation.