This is the discourse basket — the Suttapiṭaka, the recorded teachings of the Buddha, and the largest single sub-genre in the whole collection at 973 witnesses. Where the parent canonical genre is the Tipiṭaka as a whole, this is its narrative and doctrinal heart: the nikāya collections copied out for study and recitation.
The titles name the classical structure directly. The Majjhimanikāya (the Middle-Length Discourses) recurs through its divisions — Mūlapaṇṇāsa, Majjhimapaṇṇāsa — and beside it sit the Saṃyuttanikāya (Sagāthāvagga saṃyuttanikāya) and the protective discourses that cross into liturgy (the Āṭānāṭiya sutta). A large share come glossed: the nisai / nissaya titles (Nisai attha nibata, Nisai katha sattati nipata) are the sutta read through a word-by-word vernacular gloss — scripture and its teaching-apparatus bound together, which is why the sutta corpus and the grammar corpus overlap so heavily.
It is canonical to the core: 98% palm-leaf (955 of 973) and the oldest datable stratum in the collection — dated witnesses run 1501–1985, reaching further back than any other sub-genre. It is also the most heavily concentrated: Wat Sung Men alone holds 527 of the 973 (54%), with Phrae supplying 551. Read that concentration as the keystone-library effect, not as a map of where the discourses were used — every muang recited the suttas, but one library preserved the bulk of the surviving copies. Script is mostly Tham Lanna with a notable 95 Tham Lao and 237 monolingual Pali witnesses — the discourse is Pali, so a quarter of the corpus carries no vernacular at all.