In the WD of XQuery 1.1 currently being prepared for internal WG review, the 5th paragraph of Section 4.17, Function Declaration, says:

A function declaration may specify that a function is private or public (which is the default). [Definition: A private function is hidden from module import, which can not import it into the function signatures of another module. ] [Definition: A public function is accessible to module import, which can import it into the function signatures of another module. ]

EBNF production [31] allows, and the quoted paragraph suggests, that both user-defined functions and external functions are allowed to be either private functions or public functions.  However, an admittedly brief scan of the minutes recording the acceptance of private functions did not reveal whether the WG intended for this to be the case, or if only declarations of user-defined functions were to have the option specified.