Most (but not all) former CI holders were solely People's Republic of China (PRC) citizens. Many of them were immigrants from mainland China who had acquired the right of abode in Hong Kong. They did not co-hold any type of British nationality (See British nationality law and Hong Kong for details pertaining to various kinds of British nationalities). Before the handover, they were not eligible for any kinds of PRC passports. The PRC only issued Home Return Permit for them to enter mainland China only. If they did not choose to acquire British nationality through naturalisation, they could apply for the CI as a travel document from the colonial Hong Kong Government.