In general PhD defenses are open to public, I mean, in some places it isn't even valid if it wasn't public announced (by a printed paper glued to some wall, for

In general PhD defenses are open to public, I mean, in some places it isn't even valid if it wasn't public announced (by a printed paper glued to some wall, for all it's worth) and the access is restricted to the public. Of course different times require different actions but I think that some challenges remain for the _formal_ part of it.