THE VIDEVAD PROJECT:

The Vīdēvdād Project is a long term project of a small Iranistic team in the section of Indoeuropean Linguistics of the Department of Classical Philology and Indoeuropean Studies at the University of Salamanca. It is supported with the financial aid of the Spanish Ministerio de Educación y Ciencia and of the Junta de Castilla y León. Formerly this project has been carried out in the Institut für Iranistik of the Freie Universität Berlin with the collaboration of Maria Macuch and with funds of the Deutsche Forschungsgemeinschaft.

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This is from the index page:

Vīdēvdād is the only complete Nask of the Sassanian Avesta, the sacred book of the Zoroastrian religion, that has been transmitted to us in its complete Sassanian version. According to the Dēnkard the books of the Avesta were divided in three categories: gathic, ritual and legal. The legal text are divided since the Avestan in the law of Zaraθuštra (dāta- zaraθuštrahe) and the law of Vīdēvdād (dāta- vīdaēuua-). The latter handled mainly on prescriptions against nasu- "corpse" and the demoness concerning witth it (druj- nasu-).

Therefore, the Nask Vīdēvdād consisted in originally only of prescriptions in order to remove impurity from the pure elements of the creation of Ahura Mazdā. However, through many centuries of transmission, another texts about different matters have been incorporated to it, such as the mythical creation of the sixteen lands and their countercreations (V 1), Yima’s mythical kingship and his protection of the whole creation (V 2), the goddess of the earth (V 3), contracts and punishment for breaking them (V 4), proper dog’s care (V 13), sin for killing an otter and its atonement (V 14) , Θrita and the origin of the medicine (V 20) and the origin of the diseases (V 22). On the other side only V 5-12, V 16-17, partly V 18-19 and V 20 deal with different themes related to impurity and its purification and the removing of the evil forces. Thus the Sassanian text of Vīdēvdād which has arrived to our time sums 22 chapters (phl. fragard), but not all of them seem to have belonged in origin to the Vīdēvdād Nask.

This is an example of a fairly common phenomenon in the study of antiquity: medieval and later manuscripts that contain medieval texts mixed with late antique and genuinely ancient material. Pseudepigrapha manuscripts often have the same sort of mix. These Iranian texts preserve material that is of considerable interest for the study of ancient Jewish apocalypses and apocalypticism

(Via the Agade list.)