  This document describes a FITS convention developed by the IRAF Group (D.
Tody, R. Seaman, and N. Zarate) at the National Optical Astronomical
Observatory (NOAO). This convention is implemented by the fgread/fgwrite tasks
in the IRAF fitsutil package. It was first used in May 1999 to encapsulate
preview PNG-format graphics files into FITS files in the NOAO High Performance
Pipeline System. A FITS extension of type 'FOREIGN' provides a mechanism for
storing an arbitrary file or tree of files in FITS, allowing it to be restored
to disk at a later time.
