What is interesting about the play Polish Bethlehem?

Context: Lucjan Rydel, also known as Lucjan Antoni Feliks Rydel, was a Polish playwright and poet from the Young Poland movement.

Life
Rydel was the son of Lucjan Rydel, a surgeon, ophthalmologist, professor and Rector of Jagiellonian University in Kraków, and of Helena Kremer.

In 1904, Rydel wrote a nativity play, Polish Bethlehem, and staged its production in two suburbs of Kraków, Tonie and Bronowice, with local villagers as actors. It was an expression of his profound respect for rural Poland as well as the result of his flair for theatrical experimentation. Rydel left the third and the final act of his play open. In the course of history, new characters, including contemporary Polish politicians and celebrities, were added to it by various producers to make the play appeal to new audiences.

Answer: The play Polish Bethlehem, written in 1904, has the third act open to future additions, enabling future producers to add new characters to the play to update it for contemporary times.