...API for programming intermediaries on the web. In simple terms, an intermediary is a programmable proxy. More precisely, intermediaries are computational entities that lie along the HTTP stream and are programmed to tailor, customize, personalize, or otherwise enhance data as they flow along the stream

Louis Luthy's "Backwards," for example, posited that it's the user who's being browsed, while the browser software is merely a cleverly-tailored interface to lure visitors. The promise of "personalized preferences" is little more than a trick to have them divulge coveted profile data.