Wikipedia
The "Ornament of/for Realization[s]", abbreviated AA, is one of five Sanskrit-language Mahayana sutras which Maitreya—a bodhisattva or human teacher (the point is somewhat controversial) is said to have revealed to Asanga in Northwest India in the 4th century. Some scholars ( Erich Frauwallner, Giuseppe Tucci, Hakiju Ui) refer to the text's author as Maitreya-nātha ("Lord Maitreya") in order to avoid either affirming the claim of supernatural revelation, or identifying the author as Asanga himself.
The AA is never mentioned by Xuanzang, who spent several years at Nalanda in India during the early 7th century, and became a savant in the Maitreya-Asanga tradition. One possible explanation is that the text is late and attributed to Maitreya-Asanga for purposes of legitimacy. The question then hinges on the dating of the earliest extant AA commentaries, those of Arya Vimuktisena (usually given as 6th century, following possibly unreliable information from Taranatha) and Haribhadra (late 8th century).
The AA contains eight chapters and 273 verses. Its pithy contents summarize—in the form of eight categories and seventy topics—the Prajñāpāramitā sūtras which the Madhyamaka philosophical school regards as presenting the ultimate truth. Gareth Sparham and John Makransky believe the text to be commenting on the version in 25,000 lines, although it does not explicitly say so. Haribhadra, whose commentary is based on the 8,000-line PP Sūtra, held that the AA is commenting on all PP versions at once (i.e. the 100,000-line, 25,000-line, and 8,000-line versions), and this interpretation has generally prevailed within the commentarial tradition.
Several scholars liken the AA to a "table of contents" for the PP. Edward Conze admits that the correspondence between these numbered topics, and the contents of the PP is "not always easy to see..."; and that the fit is accomplished "not without some violence" to the text. The AA is widely held to reflect the hidden meaning (sbed don) of the PP, with the implication being that its details are not found there explicitly. (Sparham traces this tradition to Haribhadra's student Dharmamitra.) One noteworthy effect is to recast PP texts as path literature. Philosophical differences may also be identified. Conze and Makransky see the AA as an attempt to reinterpret the PP, associated with Mādhyamaka tenets, in the direction of Yogacara.
The AA is studied by all lineages of Tibetan Buddhism, and is one of five principal works studied in the geshe curriculum of the major Gelug monasteries. Alexander Berzin has suggested that the text's prominence in the Tibetan tradition, but not elsewhere, may be due to the existence of the aforementioned commentary by Haribhadra, who was the disciple of Śāntarakṣita, an influential early Indian missionary to Tibet. Je Tsongkhapa's writings name the AA as the root text of the lamrim tradition founded by Atiśa.
Georges Dreyfus reports, "Ge-luk monastic universities... take the Ornament as the central text for the study of the path; they treat it as a kind of Buddhist encyclopedia, read in the light of commentaries by Je Dzong-ka-ba, Gyel-tsap Je, and the authors of manuals [monastic textbooks]. Sometimes these commentaries spin out elaborate digressions from a single word of the Ornament." Dreyfus adds that non-Gelug schools give less emphasis to the AA, but study a somewhat larger number of works (including the other texts of the Maitreya-Asanga corpus) in correspondingly less detail.