The Bank of Japan just shocked markets with a policy tweak — here’s why it matters

The Bank of Japan announced Friday “greater flexibility” in its monetary policy — surprising global financial markets.

The central bank loosened its yield curve control — or YCC — in an unexpected move with wide-ranging ramifications. It sent the yen whipsawing against the dollar, while Japanese stocks and government bond prices slid.

Elsewhere, the Stoxx 600 in Europe opened…