|#define U_CALLCONV U_EXPORT2|
Do not use.
Similar to U_CDECL_BEGIN/U_CDECL_END, this qualifier is necessary in callback function typedefs to make sure that the calling convention is compatible.
This is only used for non-ICU-API functions. When a function is a public ICU API, you must use the U_CAPI and U_EXPORT2 qualifiers. ICU 2.0