Appendixes to the paper proposed three additional conventions: one to handle fields where the length of an array might vary, one to allow the vector in a field to be interpreted as a multidimensional array, and one for delimiting arrays of strings. While the Working Group endorsement of binary tables did not include these conventions, the rules that were adopted reserved a number of keywords and values specifically intended for use by these conventions. These conventions are discussed in section 5.2.
In a binary table, each row consists of a series of entries in formats specified by the header keywords. The header describes the size and data type of each entry, and, optionally, provides a label, units, and the representation for an undefined value where applicable. The length and field structure of all rows of the main table in a particular binary table extension must be the same.
Every row in a particular binary table contains the same number of entries, although the number can vary from one binary table extension to the next in a FITS file. The header is a standard FITS extension header. For each table entry it specifies
An entry may be omitted from the table but still defined in the header by using a zero repeat count in the value of the TFORMn keyword. Examples 4, 6, and 7 in Appendix A illustrate binary tables.