30 Input/output library [input.output]

30.2 Iostreams requirements [iostreams.requirements]

30.2.1 Imbue limitations [iostream.limits.imbue]

No function described in [input.output] except for ios_­base​::​imbue and basic_­filebuf​::​pubimbue causes any instance of basic_­ios​::​imbue or basic_­streambuf​::​imbue to be called.
If any user function called from a function declared in [input.output] or as an overriding virtual function of any class declared in [input.output] calls imbue, the behavior is undefined.