Minibuffer Menu Activation

When clicked within an inactive minibuffer:
  ACTION KEY
     The Hyperbole minibuffer menu is displayed for selection, by default.
     The variable action-key-minibuffer-function controls this behavior.
  ASSIST KEY
     The buffer, window and frame jump menu is displayed for selection, by default.
     You can jump to buffers categorized by major mode, jump to windows by buffer
     name, or to frames by name.  Manage your windows and frames quickly with this
     menu as well.  This is the same menu that a click in a blank area of the
     modeline displays by default since they are typically so close together.  The
     variable assist-key-minibuffer-function controls this behavior.