Hover ads, more commonly called in-page pop-ups, are a special type of pop-up ads created using Dynamic HTML, JavaScript and similar web browser technologies. Because they do not scroll with the web page, they appear to "hover" over the page, usually obscuring the content.
Background
Pop-up ads acquired a certain share of online advertising solutions and technologies. The first Internet pop-ups were created using the window.open JavaScript function, which opens a new browser window. The advertising content was presented in the window as HTML content loaded from a web address. These pop-ups were easily blocked by pop-up blockers, such as the Google Toolbar, which could be downloaded at no cost. In order to circumvent these pop-up blockers, some online advertisers tried a different method of opening pop-ups, Dynamic HTML, which is more integral to the functioning of a web-browser and thus harder to block.
Technology
Hover ads are developed around several web browser technologies but in the center of their realization is utilized DHTML, a technique where JavaScript modifies the content of the page. Using JavaScript, certain levels and objects of the browser’s DOM are manipulated to produce window-like visual DHTML elements representing hover ads or hover ad windows. The basic attribute used is a CSSHTML element attribute — position. Modern browsers implement cascading style sheets in order to separate presentation from content. The CSS technology also enables the JavaScript content of a web page to programmatically manipulate CSS attributes of various HTML elements constituting the web page's content. The first movable HTML elements were introduced in Netscape Communicator with the now-deprecated layer technology. Hover ads tend to be very hard to block by pop-up blocking software because the hover ad window is an integral part of the HTML content of the web page. Thus a software filtering the content has no algorithmic means of recognizing and removing parts of the content, either descriptive or procedural, that create, populate and manipulate the hover ad's window.
