> None of those things are present during a border crossing, for which you want to "pass" a "port". > but again, why a passport? Passport isn't only for cross

> None of those things are present during a border crossing, for which you want to "pass" a "port". > but again, why a passport? Passport isn't only for crossing the border, but to identify for the whole duration of the visit. Travellers don't have national ID documents by definition, and the passport serves this purpose. E.g. I don't know about your country, but if someone is travelling to my country, he or she is required to keep the passport in the pocket at all times and present to authorities on demand if s/he is stopped on street[1]. So when accessing women-only spaces, like applying for international sports tournaments held in other countries, this will be the document checked. If you'd like an example involving border crossing, again I don't know much about your country, but if one attempts to cross the border of mine, one of the results might be that you'd be interned in a facility for illegal migrants that for some reason won't be getting political asylum, but can't be deported to the home country either. It would then matter if the person is a man or a woman. Just asking the person is not sufficient, because we can't just allow men to identify themselves into women's wing, as that would violate rights of the women kept there and not free to go elsewhere. [1] this is contrary to citizens, who aren't generally required to have any ID on oneself, and can just say the name and number if stopped)