Explained: The mystery surrounding the exit of former Chinese leader Hu Jintao from 20th party congress

The congress, where China's next leaders are anointed, is the single most important political event for a ruling party fixated on control. Every detail, whether it is the outcome of its elections or how servers pour tea, is planned. Nothing unscripted happens. Nothing unscripted is allowed to happen. Except this year, it did. The roughly 2,000 delegates to the congress had just cast ballots for the party's prestigious Central Committee. Then, two men led Hu — who appeared reluctant to go — out of Beijing's Great Hall of the People. The moment, captured on video by journalists who had been…