Elastic order by tag value

Questions
2

The sort is built with something like this

return new FieldSort
{
    Field = Infer.Field<ReturnAuthorizationsDocument>(ff => ff.Tags[0].Value),
    Order = SortOrder.Ascending,
    Nested = new NestedSort
    {
        Path = Infer.Field<ReturnAuthorizationsDocument>(ff => ff.Tags),
        Filter = new TermQuery
        {
            Field = Infer.Field<ReturnAuthorizationsDocument>(ff => ff.Tags[0].Key),
            Value = item.Id
        }
    }
};