Matches should monotonically disappear and not get reordered as you enter more letters.
This is trivial to do on exact contexts (like start menus - why none gets this?). It's ok to wait until the user enters some letters to start showing options, it's also ok to limit the number of results as long as you say there are more somewhere. What is not ok is to show a single match, and then after the user press another key show two matches, with the first one gone.
Distance based matching can't strictly follow this rule, but if you are optimizing one, it is a good goal to get approximately right.
This is trivial to do on exact contexts (like start menus - why none gets this?). It's ok to wait until the user enters some letters to start showing options, it's also ok to limit the number of results as long as you say there are more somewhere. What is not ok is to show a single match, and then after the user press another key show two matches, with the first one gone.
Distance based matching can't strictly follow this rule, but if you are optimizing one, it is a good goal to get approximately right.