Because multiple articles can have the same title, readers find a topic by searching, rather than just by title. The authors can say who can edit their articles: the public, other authors, or only themselves. They may also choose to include ads from Google's AdSense to their knols. Knol has a policy that specifies topics that are unacceptable for the project. Relevant nudity is allowed (in most countries), but pornography, commercial or otherwise, is forbidden. Also forbidden is discriminatory or violent content. Content designed to promote businesses, products or services is allowed, but articles devoid of substantive content and created solely to generate ad revenue are not.