Columbia subject headings:
American drama--20th century--History and criticism--Congresses.
English drama--20th century--History and criticism--Congresses.
Theater--English-speaking countries--History--20th century--Congresses.
Harvard subject headings:
English drama--20th century--History and criticism--Congresses.
Theater--Great Britain--History--20th century--Congresses.
Princeton subject headings:
English drama--20th century--History and criticism--Congresses.
Theater--Great Britain--History--20th century--Congresses.