The short version
A NIMAS fileset is a source package. It is not something a student reads. It is a structured version of your title that an Accessible Media Producer converts into the format a particular student needs — braille, large print, synthetic or human audio, or digital text.
The standard exists so that conversion does not have to start from a printed page every single time. One well-structured source can be turned into many student-ready formats.
What is inside one
Three things travel together:
- A DTBook XML file marked up to the NIMAS DTD. This carries the text and, crucially, the structure — headings and their levels, chapters, lists, sidebars, tables with headers, figure groups, front matter and rear matter.
- A package file (OPF) holding the title's metadata, including the identifier that links it to the record in NIMAC.
- The images, at full resolution, correctly referenced from the XML.
The XML is the part that determines whether the conversion downstream is any good. A file that captures only the words produces a flat, unnavigable result; a file that captures the structure produces something a student can move around in.
Where alt text fits
Images that carry instructional meaning need descriptions. A labelled diagram of a cell, a chart a question depends on, a worked example — these are content, and a student who cannot see them needs their content in words.
Decorative images should be marked as decorative rather than described. Describing everything is as unhelpful as describing nothing: it fills the reading experience with noise.
Alt text is normally the part of the process that needs publisher input, because it requires knowing what the image is doing pedagogically. In our process we draft it and send it to the publisher to correct before the fileset is built.
NIMAC, and why certification matters
NIMAC is the national repository. Filesets are uploaded there by publishers or their vendors, validated, and made available to authorised users in states that have adopted them.
Uploading is not the finish line. A fileset can be rejected in validation for structural problems, metadata mismatches or image issues. Until it is certified, it is not doing anything for anyone. This is the stage that most often stalls when a publisher handles it without a vendor account and someone tracking it.
Who needs one
In broad terms: publishers supplying print instructional materials to US K–12 state and local education agencies. State adoption contracts commonly require NIMAS filesets for adopted titles, and the requirement is usually written into the purchase agreement rather than discovered afterwards.
If you are unsure whether a specific contract obliges you, the adoption documentation for that state is the place to check — the requirement and its deadline are normally stated there explicitly.
A common misunderstanding
A NIMAS fileset is not an accessible PDF, and producing one does not mean your PDF is accessible. They serve different readers: NIMAS is a source for conversion; a PDF/UA file is read directly by the end user. Many publishers need both. The good news is that both can usually be produced from the same set of source files.
Working on something this touches? Send us the details and we will tell you plainly what it takes.