code: function _assignRef(element) {
    var refString = element.getAttribute('ref');
  
    // assign element to refs object
    this.refs[ refString ] = element;
  
    // memoize ref string, clean ref attribute
    element.__refString__ = refString;
    element.removeAttribute('ref');
  }
docs: Assigns ref to refs object, removes attr and creates __refString__ reference
  @method _assignNode
  @param {Node} element
  @returns {undefined}