A more thorough explanation:

PRO POSSESSORE

Pro possessore means "as a possessor" or "by virtue of possession alone".

• John claimed ownership of the car pro possessore, as he had possession of the car keys.
• The landlord had the right to enter the apartment pro possessore, as he was the legal owner of the property.

These examples illustrate how pro possessore is used to describe a situation where someone has a right or claim based solely on their possession of something. In the first example, John's possession of the car keys gave him the right to claim ownership of the car. In the second example, the landlord's ownership of the property gave him the right to enter the apartment, even if the tenant did not give permission.