code: function toggleSubmenu(trigger, toggleFn) {
      const droplet = document.getElementById(trigger.getAttribute('aria-controls'));
  
      if (!droplet) { return; }
  
      toggleFn(droplet, (noFocus, focusTarget) => {
        const prevExpanded = droplet.getAttribute('aria-expanded');
        const wasCollapsed = !prevExpanded || prevExpanded === 'false';
        droplet.setAttribute('aria-expanded', wasCollapsed ? 'true' : 'false');
  
        if (focusTarget) {
          focusTarget.focus();
        } else if (!noFocus) {
          let active = queryAll('.dqpl-menuitem-selected', droplet).filter(isVisible);
          active = active.length ?
            active :
            queryAll('[role="menuitem"][tabindex="0"]', droplet).filter(isVisible);
          let focusMe = wasCollapsed ? active[0] : closest(droplet, '[aria-controls][role="menuitem"]');
          focusMe = focusMe || elements.trigger;
          if (focusMe) { focusMe.focus(); }
        }
      });
    }
docs: Toggles a menu or submenu