What is nationalization
This is my understanding. Usually a company has 3 types of capital: debt, preferred stock, common stock. In terms of ownership the equity holders (common stock holders) own the company. We say they borrow from the debt holders: in return they pay interest and principle to the debt holders down the road.
In the case of bankrupcy, debt holders have priority over preferred holders, preferred have priority over common, etc. (note all debt are not euqal too, some are senior than others, some are secured, some are not).