code: function click(div, target) {
      var newTab, oldTab, oldTabError;
  
      forEachEl(':scope>header:not(.tabz-enable)', function(tab) { // todo: use a .find() polyfill here
          if (tab.contains(target)) {
              newTab = tab;
          }
      }, div);
  
      if (newTab) {
          oldTab = this.enabledTab(div);
          if (!oldTab || !toggleTab.call(this, oldTab, false)) {
              toggleTab.call(this, newTab, true);
          }
      }
  }
docs: @summary Switch to the clicked tab.
  Disable the previously enabled pair and, if sucessful, enable the new tab.
  
  If the disable is fails (`onDisable` returns truthy), no visible UI change occurs. This would be the typical failure. However, if the disable is successful but the enable fails (`onEnable` returns truthy), the panel will be left in an undefined state with no tabs enabled. (This is it's "natural" state with all objects depth-sorted with last folder on top but all tabs behind.) In this case, returns `null`  in which casae you should enable some tab.
  @private
  @this Tabz
  @param {Element} div - The tab panel (`.tabz` element) that's handling the click event.
  @param {Element} target - The element that received the click.