docs: function filterCroppedNodes(node) {
    if (!node.boxObject) {
      return domUtils.DOMWalker.FILTER_SKIP;
    } else {
      if (!node.disabled && !node.collapsed && !node.hidden) {
        // Code specific to the preferences panes to reject out not visible nodes
        // in the panes.
        if (node.parentNode && (node.parentNode.localName == "prefwindow" &&
                                node.parentNode.currentPane.id != node.id) ||
            ((node.parentNode.localName == "tabpanels" ||
              node.parentNode.localName == "deck") &&
             node.parentNode.selectedPanel.id != node.id)) {
          return domUtils.DOMWalker.FILTER_REJECT;
          // end of the specific code
        } else {
          return domUtils.DOMWalker.FILTER_ACCEPT;
        }
      } else {
        // we don't want to test not visible elements
        return domUtils.DOMWalker.FILTER_REJECT;
      }
    }
  }