In some cases it’s good to customize the autocomplete for a control. For instance if you want a bold font at row 5 or different background colors according to the items. It is also possible to customize the response output from the selected item e.g if you want to return a custom object. Autocomplete list is usually initialized from textchange but can in this case be showed from button click or other event.
Read more and screenshots: http://code.msdn.microsoft.com/Customized-Autocomplete-c17bbba7