Man pages matching name al_ustr_find_cset_cstr in section 3alleg5:

al_ustr_find_cset_cstr.3alleg5.en	debian 10 / allegro5-doc
al_ustr_find_cset_cstr.3alleg5.en	debian 11 / allegro5-doc
al_ustr_find_cset_cstr.3alleg5.en	debian 12 / allegro5-doc