docs: function addMetadataValue(name, value) {
    if (typeof name !== 'string' || typeof value !== 'string' ) {
      throw new Error('metadataValues.add() takes a string name and string value');
    }
    var metaVal = {};
    metaVal[name] = value;
    return insert('/object-node("metadataValues")', 'last-child', metaVal);
  }