code: function(key) {
      var attr = this.__attrs[key];
  
      if (!attr) {
        return;
      }
  
      var value = attr.value = attr._origin;
      var setup = attr.type.setup;
  
      if (setup) {
        setup.call(this.host, value, key, this);
      }
    }
docs: Force to unsetting a value by key, use this method carefully.