What's really going on with the yuan?

Almost exactly 10 years ago, a group of US politicians accused China of manipulating its currency - keeping it artificially weak - in order to boost exports.

Today, despite the yuan being some 35% stronger than it was at the beginning of July 2003, the complaints persist.

Just last month yet another attempt was made in the US Senate to introduce a law that would punish China for its alleged exchange-rate cheating.

In the latest of our special reports on Asian currencies, the BBC's John Sudworth in Shanghai asks: what's really going on with the yuan?