Using a new "robots-nocontent" attribute, webmasters will soon be able to tell Yahoo's spiders that certain elements or sections of a page are not the real "content" of the page, and so should not be included in Yahoo's index. For example, a webmaster could flag site navigation, ads, legal disclaimers, and other non-essential elements with the attribute, leaving the main content of a page to be spidered and indexed.
It's done by creating a class attribute called "robots-nocontent," which can be used on <P> tags for individual paragraphs, as well as on <DIV> and <SPAN> container tags.
Yahoo first proposed the idea at an Indexing Summit at SES New York in 2005, the same time that Google introduced the "rel=nofollow" attribute for links. The idea was floated again at the Robots.txt Summit in New York last month, where it was well-received by site owners.
For now, the attribute will only be supported by Yahoo. It remains to be seen whether the other engines accept it as a standard, as most now have with Google's nofollow attribute.