[fitsbits] Clarification of EXTEND, please

[Thierry Forveille]

Stephen Walton writes:
 > Time to name names.  The offending piece of software is the fitsread.m
 > which The Mathworks distributes with MATLAB.  In addition to above
 > problem, Mathworks's FITS software contains another bug, this one in
 > fitsinfo.m:  it seeks 2880 bytes past an HDU which is exactly n*2880
 > bytes in length before trying to read data, and thus skips the first
 > 2880 bytes of actual data.  I have a patch for the second problem which
 > I'd be happy to share;  I haven't tried to fix the first one yet, but it
 > is probably a simple matter of checking for EXTEND = T rather than the
 > mere existence of EXTEND.
 > 
That's a first step, but even if EXTEND is present and set to T it remains
legal to not have any extension, and there could also be multiple extensions.
FITS reading software should really be prepared to recover if it does not
find an extension.