404. That’s an error.

The requested URL /bookmarks/mark?op=edit&bkmk=https%3A%2F%2Fdata.bnf.fr%2F12211821%2Faleksandr_petrovic_vasilevic%2F&title=Aleksandr+Petrovi%C4%8D+Vasilevi%C4%8D was not found on this server. That’s all we know.