ONIX (ONline Information EXchange) is a standard template that organizes electronic book information and is hosted in its own XML file. ONIX messages are formed by codelists that group together information with shared semantics and provide them with numerical values. Codelist examples for books include:
Codelist 196 contains EPUB accessibility details that provide information on an EPUB’s accessibility features. A full list of codes in codelist 196 is available here: https://ns.editeur.org/onix/en/196.
ONIX should be thought of as a supplement for schema.org accessibility and conformance reporting metadata. By using both, publishers can provide more robust accessibility metadata. Review additional ONIX resources.