The Yahoo! Design Pattern Library is an evolving set of sophisticated design guidelines for building web pages and applications. The design patterns do not require the Yahoo! UI Library components, although using the UI Library can help you more easily implement the patterns.
The Yahoo! UI Library downloads contains documentations, source files and examples of the various libraries.
While you are at it, don’t forget to read the article, Graded Browser Support By Nate Koechley, Senior Web Developer at Yahoo! Inc.