However, I've been told by French officials, in referring to the French Civil Code, that proof of French citizenship is not just a possible birthright, not inscription in what's called the Livret de famille, which is the family book, nor a passport, but rather a receipt of what's called a certificat de nationalité française, or a certificate of French nationality.
Cependant, des fonctionnaires français m'ont dit, en se référant au Code civil français, que ce qui prouve la citoyenneté française, ce n'est ni un droit de naissance possible, ni l'inscription dans le livret de famille, ni un passeport, mais la délivrance d'un certificat de nationalité française.