This is the first time I've seen this notation.

The police released him.

His release was finally decided.

He is studying in the other room.

The legislation in Japan is very complex.

He learned how to operate a mortar.

He is deepening his research on the French legal system.

He was working as a 'houkan', someone who pleases the guests at a party.

Yesterday, a gun salute was fired at the Imperial Palace to celebrate the birthday of the royal family.

He chose a straightforward method to solve the problem.