A Data Division entry begins with a level indicator or level-number
  and is followed, in order, by:

    1)  A space
    2)  The name of a data item or file connector or a screen item
    3)  A sequence of independent descriptive clauses
    4)  A separator period

  The level indicators are:

    FD  (for file description entries)
    SD  (for sort-merge file description entries)
    RD  (for report file description entries)
    DB  (for sub-schema entries)
    LD  (for keeplist entries)

  Level indicators can begin anywhere to the right of Area A.

  Entries that begin with level-numbers are either called data
  description or screen description entries depending on their context.
  The level-number values for data description entries are 01 through
  49, 66, 77, and 88.  For screen description entries the level-number
  values are from 01 to 49.