NIMAS is a technical standard used by publishers to produce source files (in eXtensible Mark-up Language (XML)) that may be used to present the content in a variety of ways and styles (such as Braille or audio books) for students with print disabilities.
The separation of content from presentation is an important feature of the NIMAS approach. In most cases, a human will need to enhance the source files to provide additional features needed by diverse learners.
The various specialized formats created from NIMAS filesets may then be used to support a very diverse group of learners who qualify as students with print disabilities. It is important to note that most elementary and secondary educational publishers do not own all of the electronic rights to their textbooks and related core print materials and a copyright exemption allows them to deliver the electronic content of a textbook and related core print materials to the NIMAC, a national repository which began operations on 12/3/06, as long as the publishers possess the print rights. The NIMAS applies to instructional materials published on or after 7/19/06.
from http://nimas.cast.org/about/nimas