This is one of several dropdown menus tested on Terrill Thompson's Dropdown Menus Test Page.
This page uses raw, unstylized strict XHTML. Structurally, the menu on this page is organized in a way that most is typical for dropdown menus. This is accessible to everyone except people who are distracted by a lot of content on the screen. In order to make this markup look and behave like a menu, the next step is to add CSS and/or JavaScript, which is where the various menu systems might introduce accessibility barriers.
To exit the menu, press tab again and you should land safely in this paragraph.