Keep in mind that if a keyword is officially "deprecated", then we are
telling software developers that they really should change their
software that creates FITS files so that it no longer writes the keyword
(unless one claims the loophole that applications that already use a
deprecated structure can continue to use it). Simply making the keyword
optional would have less impact on developers and users. For example,
if I were mandated to change CFITSIO to no longer write the EXTEND
keyword (it currently automatically writes EXTEND = T in every new FITS
file), then after projects upgrade to the new version, their FITS files
will suddenly be different than before. The change should be harmless,
but still this may cause their regression testing to fail.

arne wrote:
I don't think you can have it both ways.

If currently, you can have extensions *without* having
EXTEND=T in the initial header, then by the "once FITS,
always FITS" rule, EXTEND=T has no meaning. To me, it
originally had value because I didn't have to figure out
where the next header was (I just returned an error if
that was attempted without EXTEND=T), but if you've allowed
other uses, you have to live with it and just create more
headache for the software developers.

Deprecate it. I agree with Arnold and others.
Arne
--
__________________________________________________ __________________
Dr. William Pence
NASA/GSFC Code 662 HEASARC +1-301-286-4599 (voice)
Greenbelt MD 20771 +1-301-286-1684 (fax)