As Pope Francis continues to battle double pneumonia in hospital, his poor health is casting a spotlight on the arcane process of how the Catholic Church elects its leader. The papal "conclave" is intentionally shrouded in mystery — the term itself is Latin for "locked room" — but here are some of its rules and wrinkles: Candidates must be male and a baptized Catholic.

His age and prolonged illness have raised questions about whether he might resign, and revived interest about how papal power is exercised in the Holy See.

Francis' age and prolonged illness has revived interest about how papal power is exercised in the Holy See, how it is transferred and under what circumstances.

Pope Francis' age and prolonged illness have revived interest in how papal power is exercised in the Holy See, how it is transferred and under what circumstances.

Pope Francis continued his recovery from pneumonia Tuesday as the Vatican set in motion a nightly marathon of prayers from “his house” and allies cheered him on from afar in hopes that he might recover and get back to leading the Catholic Church.

The Holy Father's clinical condition over the past 24 hours has shown further slight improvement,” the Holy See Press Office stated.

Gandhi’s Scant Garb Bars Audience with Pope.” So read the headline of a New York Times report, from December 13, 1931, that the Vatican had cancelled a meeting between Pius XI and “the Indian nationalist leader” because the Pope thought he might be criticized “if he received the visitor in his usual scanty clothing.

And the postulator of St. John Paul II's sainthood cause, Msgr. Slawomir Oder, in 2010 published the letters Pope John Paul prepared in 1989 and in 1994 offering the College of Cardinals his resignation in case of an incurable disease or other condition that would prevent him from fulfilling his ministry.