This class is used for a Primary HDU when the SIMPLE
Card has a value of :None:None:`False`. A non-standard HDU comes from a file that resembles a FITS file but departs from the standards in some significant way. One example would be files where the numbers are in the DEC VAX internal storage format rather than the standard FITS most significant byte first. The header for this HDU should be valid. The data for this HDU is read from the file as a byte stream that begins at the first byte after the header END
card and continues until the end of the file.
A Non-standard HDU class.
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