Many memes have ``internal'' and ``external'' data representations in the sense of C enumerated ints. Other memes simply have a restricted list of legitimate values. These attributes are entered here.

Memes by themselves are often unworkably small units of information; indeed, many standard FITS keywords such as DATE are comprised of several memes. The schema permits the encoding of such structure and also provides the ability to designate bundles of memes which are all handled together. The communications between hardware and software subsystems in the instrument are represented by bundles.