This was the start of the long list of popes named Leo, Gregory and Benedict, said Melloni.

CNN: What's in a name? Clues to be found in next pope's moniker

John XXIII got away with it because he said it was in deference to his parish saint, John the Baptist, Melloni said.

CNN: What's in a name? Clues to be found in next pope's moniker

"In a church so hit by financial scandals, someone who has lived a life of poverty and rigor lays a good foundation for the papacy, " said Mr. Melloni.

WSJ: Argentina's Cardinal Bergoglio Elected Pope

Church historian Alberto Melloni says the newly available documents should provide greater context and help explain the shifts in attitude of Pius XI regarding Europen politics leading up to WWII.

NPR: Vatican Opens Pre-WWII Papal Archive

Cardinal O'Brien's resignation could prompt some cardinals to question "if it's better not to come, for the good of the church, " said Alberto Melloni, a church historian and conclave expert.

WSJ: Scottish Cardinal Resigns

He was brave to pick the name John at all, says Melloni, since the last man to hold the name is viewed as an "antipope" because he was elected pontiff during a schism in the church in the 15th Century.

CNN: What's in a name? Clues to be found in next pope's moniker