Open access to the internet is what makes Hong Kong an attractive place in China to do business, work and live for many people. It is why the United States’ online giants have a presence in the city rather than on the mainland, where they are generally banned or blocked. But the introduction of a national security law in Hong Kong has given them pause for thought, their platforms being about the free flow of information. If any determine their users have more to lose than gain through their presence and decide to quit the city, there are likely to be local reputational consequences.

That is not to contend that firms such as Google, Facebook and Twitter and apps including WhatsApp, Instagram and Telegram should be above the law. They cannot be allowed to carry information that violates rules, is discriminatory, false or harmful to others. They usually state such matters in their regulations and expect users to follow them or risk having accounts closed. The problem for many Hong Kong people familiar with the common law system is that the legislation’s unclear language and broad provisions make for uncertainty about what constitutes a violation.