[fitsbits] Abuse of EXTEND keyword

[Randall Thompson]

LC's NoSpam Newsreading account wrote:

>On Thu, 23 Aug 2007, Randall Thompson wrote:
>
>  
>
>>You are basically saying that EXTEND=F, EXTEND=T, or leaving it out 
>>completely all mean the same thing; namely, extensions may or may not 
>>exist.
>>    
>>
>
>Hence the reason for deprecation.
>  
>
As I understand the proposed standard changes and previous discussion,  
EXTEND
would not be deprecated. It would become an optional reserved keyword 
with the definition of
EXTEND=T, and possibly EXTEND=F,  both meaning extensions may or may not 
exist. I don't think
it will serve any purpose if  these changes are adopted, so I would 
think deprecation is preferable.
The advantage of deprecation would be that its use would not be 
recommended, and the definition
would not need to be clarified.

Note also that demoting it to a optional reserved keyword means it does 
not have to appear
in any particular location in the FITS header. This will also make it 
less useful in terms of
human readability. Last month we received FITS files with over 14,000 
keywords in the
primary header!

> 
>  
>
>>By the way, we get many files delivered for archiving within MAST
>>that use both the EXTEND and the NEXTEND keyword. Although not a
>>reserved keyword, NEXTEND is commonly used to describe the
>>number of included extensions. I guess we are in the minority on this,
>>    
>>
>
>Maybe you could register a "convention" about NEXTEND.
>
>Providing the number of extensions in the primary header seems a 
>very reasonable thing for me, if the file is intended to be static.
>
>What will be a file with no extension in your convention ?
>
> - no keyword at all
> - EXTEND=F and no NEXTEND kwd
> - EXTEND=F and NEXTEND=0
> - EXTEND=T and NEXTEND=0
>
>  
>
I wasn't necessarily recommending the use of NEXTEND, just stating that 
its being used by others.
If  I were to create FITS files after the proposed changes are adopted,  
with or without extensions,
I would  probably not include either keyword.