[fitsbits] once FITS always FITS

[Thierry Forveille]

Steve Allen a écrit :
> A question for those who have been around longer than I:
> 
Not sure I qualify as a true old timer (my first contact with
FITS was circa 1985), but for what it's worth my reading of "once FITS 
always FITS" is

>   Anything ever explicitly allowed can never be disallowed

plus

>   Anything not explicitly disallowed must always remain allowed
to within reason (i.e. closing contorted loopholes that pretty
much nobody ever used is fine, forbiding commonly used patterns
is not; borderline cases of course exist and then need
detailed discussion).

> In RFC 4047 we have
>   no change may be made to FITS that invalidates existing files
> but I'm not sure that's what everyone thinks.
> 
To me that's really what the rule is about: we want data archives
to remain valid+readable, and forcing a format conversion on
archive maintainers is an absolute no-no.