Do use HTML 2.0 as the lowest common denominator, then add higher level tags that will degrade gracefully. Try to use HTML more as it was intended, as structural markup, rather than layout tool. Do offer documents, if possible, also as text files. This can be especially important if the website utilizes more advanced technologies that are incompatible with older browsers, specialized equipment used within the disabilities community, or from secured computers in public access locations with limited capabilities. Avoid using frames.
Usability studies find users particularly frustrated by frames.
In addition, many browsers do not support frames adequately, if at all. The power of the Web is in its universality. Access by everyone regardless of disability is an essential aspect. Tim Berners-Lee, W3C Director and inventor of the World Wide Web. The W3C's commitment to lead the Web to its full potential includes promoting a high degree of usability for people with disabilities.