SHANGHAI, Aug 20 (Reuters) - China’s stock exchanges are revising underwriting rules for Shanghai’s STAR Market and Shenzhen’s ChiNext board in a bid to improve the pricing mechanism for initial public offerings (IPOs). The Shanghai Stock Exchange and the Shenzhen Stock Exchange published separate draft rules that will tighten scrutiny on investors’ behaviour during the IPO quotation process. Certain rules during the process are also being tweaked. (Reporting by Shanghai Newsroom; editing by Jason Neely) Our Standards: The Thomson Reuters Trust Principles.