Touch Portal will send messages when a list of choices value is changed. Your software needs to handle these messages and act on it if you want to use this functionality. This is especially useful when your action (or event/connector) has multiple drop down list boxes where selecting an item in the first needs to repopulate the second.
The values attribute is present from API 7. It holds all user input in the action the list belongs to. Be aware that this is during editting so it could be no values are input yet or all are. This array does not necessarily be in the same order as the data is in the action itself.