> If there are no subsequence/substring matches, it can optionally fall back to approximate matches. This is rarely necessary to provide
Supporting proximity matches is critical for anything dealing with city names, landmarks, events, person or commercial names, etc, where typos and mixed language input are a normal occurrence. This applies to almost every e-commerce site out there.
> Matches should be sorted alphabetically
This is countered by a few other of his own rules, such as 'prefix matches come first', 'exact matches come first'. Again, in some applications the best behaviour might be sorting by distance, recent use, relevance, popularity, ratings. Sorting is entirely domain-specific.
> If an option is highlighted, never change it, even if new data is loaded
I don't get this one. If I have the second item selected, and search for a completely new term, should the item remain wedged in the new results at the same position?