docs: function addToSchema(index, properties) {
          this[_privateKey]._schema[index] = normalizeProperties.call(this, properties, index);
  
          defineGetter.call(this[_privateKey]._getset, index, this[_privateKey]._schema[index]);
          defineSetter.call(this[_privateKey]._getset, index, this[_privateKey]._schema[index]);
      }