docs: function _removeMappedFields(mapping, path) {
      if (typeof path === 'number') {
          delete mapping[path];
          return mapping;
      }
      var keys = path.split(_separator);
      if (keys.length <= 1) {
          delete mapping[path];
          return mapping;
      }
      return _removeMappedFields(
          mapping[path[0]],
          keys
              .slice(1)
              .join(_separator)
      );
  }