“Autocomplete” is one of those words that modern web designers and programmers sometimes use and then wave their hands like that one word actually describes a complete user interaction without saying anything further: “They get to the message window, then there’s an autocomplete box.” But that’s actually a pretty broad category these days.
Polihood's message autocomplete - a Boxed Build-A-List.
There are a few distinct autocompleter mechanisms popular on the Web. While they look similar at first glance, their UI function is actually completely different, and they each meet totally different user interaction needs. Since there hasn’t been a lot of explicit talk about the differences in these types of autocompletes, it can be a source of confusion when the folks on a project have different assumptions. Make sure you’re on the same page as the other designers and/or programmers when you talk about autocompletes.
Here are the three main types of popular autocompleters: