docs: function(selector, context) {
    this.selector = selector;
    if (typeof context == 'function') {
      this.context = null;
      this.asyncExecute(null, null, context);
    }
    else {
      this.context = context;
    }
  
    this.instance = -1;
    this.index = -1;
    this.length = -1;
  }