Avestan language
With the notable exception of the "Yasht"s, almost all surviving Avestan texts have their Middle Persian "zand", which in some manuscripts appear alongside (or interleaved with) the text being glossed. These glosses and commentaries were not intended for use as theological texts by themselves but for religious instruction of the (by then) non-Avestan-speaking public. In contrast, the Avestan language texts remained sacrosanct and continued to be recited in the Avestan language, which was considered a sacred language.