Yahoo! has a tag that will help Web designers and webmasters control what text Yahoo! robots will reference and make searchable. The tag is called class="robots_nocontent", this tells Yahoo's spider slurp to ignore the content controlled by this class attribute.
With robots.txt, site owners can only specify whole pages or directories to exclude. Yahoo has added a new twist, enabling site owners to specify which sections of an entire page to exclude with the new robots_nocontent tag.
For example, you may wish to tell Yahoo! to ignore the footer or sub menus on your page and to focus on the test content within the page. Any parts of the page containing a nocontent class will still be crawled, but Yahoo! won't use this information to calculate relevant keywords.