Man pages matching name unicode::iconvert::convert_tocase in section 3:

unicode::iconvert::convert_tocase.3.en	debian 10 / libcourier-unicode-dev
unicode::iconvert::convert_tocase.3.en	debian 11 / libcourier-unicode-dev
unicode::iconvert::convert_tocase.3.en	debian 12 / libcourier-unicode-dev