China's stock market is one of the best in the world in 2019

After the worst performance in a decade in 2018, China's stock market has been one of the best performers in the world in 2019.

• Its outperformance of the U.S. has largely been driven by gains this month, which has seen onshore Chinese stocks rise a full 10% more than the S&P. Of note was Monday's 6% gain after President Trump delayed a planned tariff increase on Chinese goods.

Driving the news: Today, index maker MSCI will announce its decision on increasing the number of onshore Chinese companies in its indexes. So far, just 5% of the so-called A shares are included, but investors expect to see that rise to around 15%.

Details: A shares would be added to the MSCI World and China indexes as well as the Emerging Markets index, which tracks $1.9 trillion of securities.

• If and when A shares are fully included in MSCI's indexes, a full 40% of the MSCI Emerging Markets Indexwould be made up of Chinese stocks.

The bottom line: Raising the level of A shares would underscore China's progress in opening up its markets despite tensions with Washington, less than a year after MSCI admitted Chinese A shares to its index for the first time — after 3 rejections.

Go deeper: China's unclear economic outlook