Brock is made of several packages and each have their own set of classes. The UML documentation of this project is generated with wonderful tool made by TogetherSoft called simply Together. This CASE tool is used to maintain both the code and the documentation. A free version of this software can be obtained directly from their web site at www.togetherSoft.com
So these diagrams are all structured with the Java class hierarchy. A very usefull navigator let you choose the desired diagram. Start your exploration here.
By the way, Internet Explorer gives a better experience since it offers a second tab in the navigator applet that shows an overview of the diagram. A shame we can't have that one with Netscape :-(.