- Field name: Each word in the first non-comment (non-#) line is the name of a field.
- Field type: Each word in the second line is the type of the corresponding field. Types can be `s` (string), `b` (byte), `B` (boolean), `w` (word, 4-bytes integer) or `a` (array of bytes, treated as binary data). An array type is written as two letters: the letter `a` followed by the type of elements. For example, `ai` is an array of integers, and `ab` is an array of bytes.
- Field comment: Each word in the third line is a comment about the corresponding field.