code: function toggleSubTree(elem, fold) {
          fold = typeof fold !== 'boolean'
              ? !elem.hasClass('members-folded') // reverse of current state
              : fold;
  
          var parent;
          if (fold) {
              parent = elem.addClass('members-folded').parent();
              parent.find('.item-members:first').addClass('no-height');
              parent.find('.item-inner > img.item-tree-parent').attr('src', 'img/tree-folded.png');
              // Even if only one is folded, set state as folded and visual state
              // for fold toolbar button.
              setFoldState(true);
          } else {
              parent = elem.removeClass('members-folded').parent();
              parent.find('.item-members:first').removeClass('no-height');
              parent.find('.item-inner > img.item-tree-parent').attr('src', 'img/tree-parent.png');
          }
      }
docs: Toggles the sub-tree of the given root member.
  @private
  
  @param {JQuery} elem - JQuery element (for the root memeber) whose
  sub-tree will be toggled.
  @param {Boolean} [fold] - If this value is defined, target element's
  sub-tree folded state will be set explicitly, instead of toggling the
  current state.