[fitsbits] structurally compliant FITS

[Mark Calabretta]

On Fri, 26 Jun 2015 14:06:10 -0700
Rob Seaman <seaman at noao.edu> wrote:

Hi Rob,

>I suppose you are suggesting that since pretty much everything is
>optional after the first 2880-byte record that we might omit the word
>optional for more particular cases throughout the standard?

Yep.  Describing parts of the standard as "optional" is not particularly
meaningful, nor helpful.  Specifically, I was responding to Lucio's
"conventions which are parts of the standard, while remaining optional".  
 
> > Ignoring INHERIT or CONTINUE potentially produces *wrong* answers
> > without providing even a hint that anything is wrong.  That's not
> > what I call "harmless".
> 
> In previous cases of modifying the standard we have jiggered things
> such that new-format files might either be invisible to unmodified
> software (e.g., relying on the extra appended record gimmick), or
> rather would cause unmodified software to abort (e.g., negative
> BITPIX values).
> 
> But several of the conventions are already perfectly legal FITS.  And
> projects already use INHERIT, for instance.  Improving the
> documentation and hooks for recognizing such usage will be surely
> "less harmful", if not "harmless", right?

Again, I was only responding to the statement, made repeatedly in
various ways by several people, that INHERIT may be "ignored" and doing
so is "harmless".

As you suggest, inheritance would better be implemented in such a way
that ignoring it causes an error.  However, that would probably require
creating new syntax, and that's not something that conventions can do.

Regards,
Mark