docs: function _filter(data, schema) {
      if (typeof data !== 'object' ||
          data === null ||
          schema === null) {
          return data;
      }
      if (schema instanceof Array) {
          return _filterByArraySchema(data, schema);
      }
      if (typeof schema === 'object') {
          return _filterByObjectSchema(data, schema);
      }
      return data;
  }