Sometimes a command doesn't have a completion installed—or syntactically could accept a whole bunch of types of arguments, rendering completion next to useless. For instance, "git checkout" can take the name of any git-tracked file or the name of any ref or other tree-ish. It can also take some option flags. That's a lot of possible completions.
Knowing that I want to complete—say—a branch name, is there a way to bind a key to complete against or display a menu of branch names? (And likewise for any category of completion.)
That seems possible and useful, but I haven't seen it done.