///<summary>Default list of fields to extract and return from the _source field, can be overridden on each sub-request</summary>
internal static BulkRequestParameters _SourceInclude <T>(this BulkRequestParameters qs, IEnumerable <Expression <Func <T, object> > > source_include) where T : class =>
qs.AddQueryString("_source_include", source_include.Select(e => (Field)e));
///<summary>Default comma-separated list of fields to return in the response for updates, can be overridden on each sub-request</summary>
internal static BulkRequestParameters _Fields <T>(this BulkRequestParameters qs, IEnumerable <Expression <Func <T, object> > > fields) where T : class =>
qs.AddQueryString("fields", fields.Select(e => (Field)e));