Annex G (informative) Ill-formed, no diagnostic required [ifndr]

G.7 [module]: Modules [ifndr.module]

G.7.3[ifndr:module.unit.unexported.module.partition]
Specified in: [module.unit]

1
#
If a module partition of a module that is a module interface unit but is not directly or indirectly exported by the primary module interface unit ([module.import]), the program is ill-formed, no diagnostic required.
2
#
[Example 1: 

Translation unit #1:export module M; // primary module interface unit export import :A;

Translation unit #2:export module M:A; // OK, directly exported by M export import :B;

Translation unit #3:export module M:B; // OK, indirectly exported by M

Translation unit #4:export module M:C; // IFNDR, not directly or indirectly exported by M — end example]