We don't know how it's legal, since the vast majority of the rooms, apartments and other private accommodation listed on the AirBnB website presumably operate without having received permits or having jumped through the notoriously opaque hoops of Slovene bureaucracy (not to mention the small matter of taxes). Despite those little legal issues millions of travellers (us included) have fully embraced the sharing (ie grey) economy via AirBnB as it offers excellent value accommodation with several hundred full apartments and another hundred or so private rooms currently available in Ljubljana.