o move backward through the list.  This
     command is intended to be bound to <TAB>, but is unbound by
     default.

'menu-complete-backward ()'
     Identical to 'menu-complete', but moves backward through the list
     of possible completions, as if 'menu-complete' had been given a
     negative argument.

'delete-char-or-list ()'
     Deletes the character under the cursor if not at the beginning or
     end of the line (like 'delete-char').  If at the end of the line,
     behaves identically to 'possible-completions'.  This command is
     unbound by default.