[fitsbits] Clarification of EXTEND, please

[Jonathan McDowell]

Stephen, the standard is pretty clear on this
e.g.
http://archive.stsci.edu/fits/fits_standard/node39.html

Even if EXTEND = T, it only means that there *may* be 
further extensions, so doing something that will die if
extensions are not present is always incorrect.
You should be prepared to handle the possibility of EOF
when checking for extensions; it's not that hard to do.

EXTEND=F is in fact a guarantee that further extensions
are NOT present and by my reading of the standard is
a perfectly legal thing to do.
 - Jonathan McDowell
   jcm at cfa.harvard.edu