IFF files are extensible and forward/backward compatible:

  o Chunk contents should be designed for compatibility across
     environments and for longevity.  Every chunk should have a path for
     future expansion; at minimum this will be an unused bit or two.

  o The standards team for a FORM type can extend one of the chunks that
     contains a structure by appending new, optional structure fields.

  o Anyone can define new FORM types as well as new chunk types within a
     FORM type.  Storing private chunks within a FORM is OK, but be sure
     to register your activities with Commodore Applications and Technical
     Support.

  o A chunk can be superseded by a new chunk type, e.g., to store more
     bits per RGB color register. New programs can output the old chunk
     (for backward compatibility) along with the new chunk.

  o If you must change data in an incompatible way, change the chunk ID or
     the FORM type ID.