code: func (item *MultiGetItem) VersionType(versionType string) *MultiGetItem {
  	item.versionType = versionType
  	return item
  }
docs: // VersionType can be "internal", "external", "external_gt", or "external_gte".
  // See org.elasticsearch.index.VersionType in Elasticsearch source.
  // It is "internal" by default.