HONG KONG :At least two dozen Chinese companies have confidentially filed for listing in Hong Kong this year and more are preparing to do so, two industry sources said, following a new rule permitting private filings at a time of heightened market volatility. The Hong Kong exchange's rule for U.S.-style confidential filings, which allows certain companies to keep their business plans and financials under wraps in the initial stages of their stock market debut process, was implemented in May.