Welcome to browser hell. There are three major visual browsers, Internet Explorer, Netscape Navigator, and Opera. None of these allow you to use the entire range of accessibility tags. Nor is the support for the usable ones consistent. Platform dependancies create rendering issues.
Lynx is a text browser.
Limited formatting and no visuals allowed here. Screen Readers require a whole new mindset in respect to using tables for presenting content. Testing, Testing, Testing. You can build the cleanest pages possible and validate them, but unless you test them in every browser you can get your hands on and get your friends who work in different environments to test them, you will not be sure. Building valid websites is easy.