A page update handler, which may be loaded by a web browser as part of a web page, adds functionality for dynamically updating the web page with content supplied by a content server. The content may be related to a particular item detected on the web page by the page update handler, such as a link that matches a link signature, or a recognized keyword or phrase. The content server may operate in a different Internet domain from the server that servers the original web page, and may supply content for display on web pages of many different independent web sites. In one embodiment, an operator of a web site that is separate from the content server can enable the display of content from the content server on the site's web pages by merely adding an update handler tag to one or more corresponding HTML documents.