Man pages matching name font_has_alpha in section 3alleg4:

font_has_alpha.3alleg4.en	debian 10 / allegro4-doc
font_has_alpha.3alleg4.en	debian 11 / allegro4-doc
font_has_alpha.3alleg4.en	debian 12 / allegro4-doc
font_has_alpha.3alleg4.en	debian 13 / allegro4-doc