29 Input/output library [input.output]

29.2 Iostreams requirements [iostreams.requirements]

29.2.1 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.