The extended header holds more information than is carried in the standard header and expands as needed. It contains ASCII or numeric data in a free format accessed by a keyword. Each header field consists of a keyword followed by the field value. Except for several predefined keywords, a user or application is free to define its own keywords and store whatever data it wishes in the extended header. If you plan to share your data or your application, you should choose distinctive keywords and publish them for everyone to see.
At the NeXtMidas shell prompt (nM>), type EXPL KEYWORD
to view
reserved keywords and to learn how to add, modify or delete keywords.