Birds:
Result:

The Autocomplete widgets provides suggestions while you type into the field. Here the suggestions are bird names, displayed when at least two characters are entered into the field.

The datasource is a server-side script which returns JSON data, specified via a simple URL for the source-option. In addition, the minLength-option is set to 2 to avoid queries that would return too many results and the select-event is used to display some feedback.