Abstract: A system and method is described that facilitates the publication of documents, such as Web pages, that include user-viewable elements, such as online advertisements, that automatically expand beyond a region initially allocated to such user-viewable elements in response to certain user input. In an embodiment, ad presentation code and event detection code are included within a document. The ad presentation code, when executed by a client computer, causes an expandable user-viewable element to be presented within a first allocated region of the document. The event detection code, when executed by the client computer, monitors for an occurrence of an event and responsive to detecting the occurrence of the event, obtains additional user-viewable content from the expandable user-viewable element and presents the additional user-viewable content within a second allocated region of the document.