function toggleSubmenu(oMenu, iItemId) {

   // Close the currently open menu and hide the submenu (if available).
   if (iOpenedId != -1) {

      // Close the menu.
      document.getElementById('menu_' + iOpenedId).className = '';

      // Hide the submenu.
      if (document.getElementById('subMenu_' + iOpenedId) != null) {
         oSubmenu = document.getElementById('subMenu_' + iOpenedId).style.display = 'none';
      }

   }

   // If the user clicks something that was not yet opened, open it.
   if (iOpenedId != iItemId) {

      // Activate the clicked menu.
      document.getElementById('menu_' + iItemId).className = 'active';

      // Display the submenu.
      if (document.getElementById('subMenu_' + iItemId) != null) {
         oSubmenu = document.getElementById('subMenu_' + iItemId).style.display = 'block';
      }

      // The selected item is now the opened one.
      iOpenedId = iItemId;

   // If the user clicked the same menu as that was opened, no menu is open anymore.
   } else {

      // Therefor set the "iOpenedId" to -1, meaning -> no menu is opened.
      iOpenedId = -1;

   }

}