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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.