...the candidate functions are selected as follows:

• The conversion functions of S and its base classes are considered, except that for copy-initialization, only the non-explicit conversion functions are considered. Those non-explicit conversion functions that are not hidden within S and yield type “lvalue reference to cv2 T2” (when 9.4.4 [dcl.init.ref] requires an lvalue result) or “cv2 T2” or “rvalue reference to cv2 T2” (when 9.4.4 [dcl.init.ref] requires an rvalue result), where “cv1 T” is reference-compatible (9.4.4 [dcl.init.ref]) with “cv2 T2”, are candidate functions. For direct-initialization, those explicit conversion functions that are not hidden within S and yield type “lvalue reference to cv2 T2,” or “cv2 T2” or “rvalue reference to cv2 T2,” respectively, where T2 is the same type as T or can be converted to type T with a qualification conversion (7.3.6 [conv.qual]), are also candidate functions.