The XHTML 1.0 Frameset is used when Frames are to partition the browser window into two or more frames. The Frameset DTD includes everything in the transitional DTD plus frames as well.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">