Raniero Cantalamessa, preacher to the Pontifical Household, held the first meditation as outlined by the Apostolic Constitution, Lombardi said.

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Under the terms of the Pope's proposed Apostolic Constitution, groupings of Anglicans would be able to join "personal ordinariates".

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"The Personal Ordinariates were established by an Apostolic Constitution, the highest form of legal document in the Catholic Church, " he said.

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The document the cardinals are studying is the Apostolic Constitution of Pope John Paul II, known as the Pastor Bonus, which was published in 1988.

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Though Benedict left the rules greatly untouched, experts on the Church's constitution will comb through the section on the "Vacancy of the Apostolic See and the Election of the Roman Pontiff" (how to elect a new pope when the office is vacant) and interpret proper protocol for the election.

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