How to use the pouchdb-errors.DOC_VALIDATION.message function in pouchdb-errors

}];
    }
  }

  invalidIdError(doc._id);

  doc._rev = nRevNum + '-' + newRevId;

  var result = {metadata : {}, data : {}};
  for (var key in doc) {
    /* istanbul ignore else */
    if (Object.prototype.hasOwnProperty.call(doc, key)) {
      var specialKey = key[0] === '_';
      if (specialKey && !reservedWords[key]) {
        var error = createError(DOC_VALIDATION, key);
        error.message = DOC_VALIDATION.message + ': ' + key;
        throw error;
      } else if (specialKey && !dataWords[key]) {
        result.metadata[key.slice(1)] = doc[key];
      } else {
        result.data[key] = doc[key];
      }
    }
  }
  return result;
}