Tibetan has described its own grammar for a very long time, and the description is still the framework in which the language is taught inside the tradition.
Two short root texts stand at the head of it. The first, known as the Thirty, sets out the letters and the elements of the syllable. The second, known as the Guide to Signs, treats the prefixes and the rules governing which particle form follows which final. Both are attributed by tradition to Thonmi Sambhota, the seventh-century minister credited with bringing the script from India, and both are very brief, in verse, and effectively unusable without a commentary. Around them has grown a large commentarial literature, and it is through those commentaries that the material is actually studied.
Modern scholarship treats the attribution with caution and the texts as later than the tradition holds, without disputing that a grammatical tradition of considerable age exists. The vocabulary this atlas uses for the letters comes from that tradition and not from Western linguistics: sum cu for the thirty consonants, dbyangs for the vowel signs, sngon jug and rjes jug for prefix and suffix, mgo can and btags for superscript and subscript, ming gzhi for the root letter.
Using the tradition and its own terms is a choice with a consequence. It describes the script as its users describe it, and it does not flatten those categories into the nearest European equivalent.