The expression 'Hong Kong Letters Patent' is most commonly used to refer to the Hong Kong Letters Patent 1917, one of the principal constitutional documents of British Hong Kong (others being the Hong Kong Letters Patent 1960, the Hong Kong Letters Patent 1982, the Hong Kong Letters Patent 1991 (No. 1), and the Hong Kong Royal Instructions 1917); however, it may also refer to any other Hong Kong Letters Patent or be used as a generic term covering all Hong Kong Letters Patent.