On page 101 of the book we say, “So we wrote an open source menu script of our own, which you can download from [this site].”
Let me just say that as the book went to press we were still working out some kinks to the system. What we came up with was far less robust and usable than what the folks at Yahoo! and Dojo have been working on. Therefore, we defer to those libraries.
In January 2009, Wendy summarized the results of testing eight menuing systems across a variety of variables in a Menu Testing Matrix. The conclusion favors the YUI menu component and Dojo/Dijit menu system in terms of licensing (Free BSD-based licensing), access technology support, ARIA integration, and usability (especially in terms of keyboard navigation and replication of system menu behaviors).