Rules for Autocomplete

I see this frequently enough that, rather than complain about them individually, I though I’d just write down the set of rules they often break. There may be cases where some of these rules aren’t the best thing to do, but there should be a good reason for breaking one of these rules (for example, some of these rules don’t apply if a field must be filled with a value from a fixed set, like the list of US states). Following these rules should always result in at very least a sane experience:

There are some optional features that make sense in certain kinds of autocompletion and not others.

Source: jeremymikkola.com