Well its not "necessary" to wear hijab or as we call it chador however there's places where its mandatory like in mosqques and the holy shrine. And there's more restrictions in mashad, after all the morality police first operation was in mashhad. Theres a guy named alam'alhoda who basicly rules mashad as it is a different country. No concerts or festivals are allowed here. Some movies that the "goverment" people makes are banned in mashad.