Tznius and Krias Shema

There is no Hilchos Tznius in Shulchan Aruch with regard to women's dress. Why not? It can't be that there is no issue at all because in Hilchos Krias Shema 75 the whole Siman discusses what is considered and "Erva" in which Krias Shema cannot be recited at close proximity. The explanation is that it is not Tznius to discuss how women should or shouldn't dress in and of itself. The whole concept is only discussed in the context of other Halachos where we need clarity. That is, in and of itself, a shiur in Hilchos Tznius.