code: function insertNode(parent, index, newNode, replace) {
    if (!parent.childNodes) {
      parent.childNodes = [];
    }
    var newNodes = [];
    var removedNode = replace ? parent.childNodes[index] : null;
    if (newNode) {
      if (isDocumentFragment(newNode)) {
        if (newNode.childNodes) {
          newNodes = Array.from(newNode.childNodes);
          newNode.childNodes.length = 0;
        }
      } else {
        newNodes = [newNode];
        remove(newNode);
      }
    }
    if (replace) {
      removedNode = parent.childNodes[index];
    }
    Array.prototype.splice.apply(parent.childNodes, [index, replace ? 1 : 0].concat(newNodes));
    newNodes.forEach(function(n) {
      n.parentNode = parent;
    });
    if (removedNode) {
      removedNode.parentNode = undefined;
    }
  }
docs: Inserts `newNode` into `parent` at `index`, optionally replaceing the
  current node at `index`. If `newNode` is a DocumentFragment, its childNodes
  are inserted and removed from the fragment.