Complex sentence: Manuscripts must satisfy certain linguistic, chronological and cultural criteria to be incorporated into the canon: they must not significantly depart from the language and tradition of Constantine and Methodius, usually known as the "Cyrillo-Methodian tradition".
Split into simpler sentences: Manuscripts must satisfy certain linguistic, chronological and cultural criteria to be incorporated into the canon: they must not significantly depart from the language and tradition of Sts. Cyril and Methodius, usually known as the "Cyrillo-Methodian tradition".