After you've made the decision to use frames on your site, you need to know the XHTML elements that make it possible. The next several sections show you how to create framed pages and how to provide alternatives for those who can't view frames.
To implement a frameset in XHTML, you must be using the XHTML 1.0 Frameset Document Type Definition (DTD). The XHTML Strict and Transitional DTDs will not support the frame-related elements.
To incorporate the Frameset DTD into your documents, the first line of code in your XHTML files should be
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/frameset.dtd">
This indicates to the browser that it should use the XHTML Frameset ...