When the list narrows to a single entry, the single options becomes highlighted. The form can then be submitted by pressing "Enter". If the keyboard focus is set to the search term input box on page load, then this becomes a fast, entirely keyboard-based interface. Interfaces like these are used by the telephone directory operators you reach when you call 411. One of my clients uses this interface to manage his 2000+ patients. That interface has an additional "search first name" option, which is activated whenever the secretary types a comma as the first character of the search term.
In this particular example, clicking on a function name (or pressing enter) will jump to the PHP reference page for that function. (The PHP website has recently implemented their own auto-completing combobox on their search page.) Jumping to a page is a common behaviour, but you can change it as you need.
|Search For Function Name|