This is the infrastructure of literacy: the grammatical and lexical apparatus by which the north learned to read Pali and to write its own Tham script. The catalogue files all 389 witnesses under a single clean label, Philology, and the titles resolve into three tight families.
First, the saddā / vyākaraṇa tradition — Pali grammar proper, the Kaccāyana school inherited from Pagan: Saddabhedacintā, the Saddavutti and its ṭīkā, the treatises on sandhi (euphonic combination — Pali sūt sondhi, Sap santhi), and the Vuttodaya, the classic manual of Pali prosody, here both bare and as a nissaya (Nisai wuttotanya). Second, the lexicography — the sap (from Sanskrit śabda): Pali-and-vernacular word-lists and glossaries, Nama sangkaha, Nama sap pali palivan, the collected vocabularies a student needed at his elbow. Third, and most immediately useful to a modern reader, the vernacular primers: manuals like Tamra rian akson Lanna, "a treatise for learning the Lanna letters" — the schoolbook by which the script itself was taught.
So this is the meta-genre. Every other corpus in the collection — canonical, chronicle, wichaa — stands on this one, because none of it is legible without the grammar and the glossary that made Pali construable in the north. It matters to the esoteric material in a specific way: the saddā sciences are also what let a ritualist parse and compose the Pali katha (spell-formulae) at the heart of Magic & Ritual — grammar is the key that turns a line of Pali into a working spoken formula.
This is the most technically "canonical" genre in the collection by its physical and linguistic profile. It is 97% palm-leaf — the highest of any genre, a pure scholastic support — and it carries the highest share of monolingual Pali anywhere in the collection (38%, against 59% Pali-and-Lan Na): a grammar of Pali is very often written in Pali. The dated witnesses cluster hard in the 19th century (202 of 267), tailing back to the 16th.
Geographically it repeats the canonical pattern — Phrae 50%, and Wat Sung Men alone supplying 40% of the genre — which is a fact about one library, not one region (see below).