FITS Foreign File Encapsulation Convention

A FITS extension of type 'FOREIGN' (henceforth a "FOREIGN file extension" or just "FOREIGN extension") 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. Each FOREIGN extension contains a single file. This mechanism also provides a means for associating a group of FITS extensions of any type. Certain of the file attribute keywords can be included in the header of any FITS file or extension to support such things as storing a directory tree containing images, tables, and other non-FITS types of files in a multi-extension FITS file, and later restoring the whole tree to disk. The motivation for this extension is to allow an implementation based on the FITS multi-extension mechanism to encapsulate and pass non-FITS data. The FOREIGN extension may be used to store a file from any type of operating system (e.g. UNIX or Windows), however some of the specific file attributes that are recorded in the FOREIGN extension keywords may not map completely between different systems (e.g. the UNIX filemode string that may be recorded in the FG_FMODE keyword does not have an exact counterpart under Windows).