Wikipedia
SDXF
SDXF (Structured Data eXchange Format) is a data serialization format defined by RFC 3072. It allows arbitrary structured data of different types to be assembled in one file for exchanging between arbitrary computers.
The ability to arbitrarily serialize data into a self-describing format is reminiscent of XML, but SDXF is not a text format (as XML) — SDXF is not compatible with text editors. The maximal length of a datum (composite as well as elementary) encoded using SDXF is 16777215 bytes (one less than 16 MiB).