China has boosted security in Beijing’s Tiananmen Square, ahead of Thursday’s anniversary of the killings in 1989. Many dissidents say they have been told to leave Beijing or are confined to their homes. During that massacre, Hundreds, possibly thousands, of people died in the Tiananmen crackdown, and open discussion of the events of 20 years ago remains taboo in China. Even in Hong Kong, where freedom of expression is guaranteed, some dissidents have been denied entry. Xiang Xiaoji, now a US citizen, was trying to come to Hong Kong on Wednesday to join commemorative events being held to mark the anniversary. But he was refused entry and returned to New York. This is the experience of many such people who have been marked as dissidents by the chinese government.