Let's say I'm using an autocomplete to choose a country: I know I can format the list with a template, but at the moment I can't have the inner value of the widget to be the ISO code and the input text value to be the description + ISO country code.
For example, the user types "ita" in the input box, the list shows an element with "[flag] Italy". When the user clicks on that row, the input box changes to "Italy - IT", and the Autocomplete istance would return "IT".