///<summary>A list of fields to extract and return from the _source field</summary>
internal static DocumentExistsRequestParameters _SourceInclude <T>(this DocumentExistsRequestParameters qs, IEnumerable <Expression <Func <T, object> > > source_include) where T : class =>
qs.AddQueryString("_source_include", source_include.Select(e => (Field)e));
///<summary>A comma-separated list of stored fields to return in the response</summary>
internal static DocumentExistsRequestParameters _StoredFields <T>(this DocumentExistsRequestParameters qs, IEnumerable <Expression <Func <T, object> > > stored_fields) where T : class =>
qs.AddQueryString("stored_fields", stored_fields.Select(e => (Field)e));