PDF/A-3b (ISO 19005-3, level B): PDF/A-2b, except that a file of any kind may be embedded when it is an associated file: each
embedded file's specification has an AFRelationship, is listed in an AF array, and its stream names a MIME type.
PdfA3b = 3
ISO 19005-3, 6.8 (veraPDF PDF/A-3B validation profile, rules 6.8-1 to 6.8-4).