The last letter of the alphabet writes the plainest sound in it. The ordering runs by place of articulation through the stops, from the back of the mouth to the lips, then gathers the nasals, the glides, the liquids and the sibilants, and the glottal fricative comes after them all. The gap between the words and the writing is the central fact about this alphabet, and it runs in both directions. The Avesta is far older than the script, and every surviving manuscript is far younger, so the script sits between two long stretches of transmission and belongs wholly to neither.
The Zoroastrian communities that carried these manuscripts, in Iran and in western India, are small, and the copying was sustained by priestly families rather than by any large institution. That the texts survive at all is a consequence of that continuity. In the digital record the letter is encoded at U+10B35 AVESTAN LETTER HE. The block covers the letters together with a small set of punctuation marks used in the manuscripts. Standardising it settled, for digital purposes at least, a question the printed editions had answered in several different ways, which is how many letters the alphabet has. What this alphabet holds is a performance. The atlas describes it and does not instruct in it: the recitation belongs to the community that maintains it, and the interest here is in what the script was built to do and how well it did it.