Typeahead is a feature, in which you start typing a word (like a menuitem, or for a link in webpage) and the system finds the first occurence of that word. This is already implemented in Firefox and many other programs. And now it's in Fluxbox
People using mostly keyboard benefit the most from typeahead. In fluxbox, currently the menu has a typeahead feature, incoming is focusing windows with typing their title.
So, you open the menu, and start typing the item you want, let's say "Applications". You should see the word(s) getting underlined. If there is multiple items with same kind of name, you can switch between them by pressing tab. Shift + tab goes other way around.
If you mistype a word, backspace erases characters back to where it matches other items. So not just 1 character, but to a point when there was multiple matches. When pressing backspace with no selection (nothing underlined) the current submenu gets closed.
Enter opens a submenu or executes the item/application selected.
To close all menus, press esc.