code: function fragment(arr, store) {
    var el = document.createDocumentFragment();
    for(var i = 0, l = arr.length; i < l; i++) {
      el.appendChild(render(arr[i], store));
    }
    return el;
  }
docs: Render fragment of virtual dom.
  
  @param {Array} arr
  @param {DataStore} store
  @return {DocumentFragment}
  @api private