[fitsbits] reopening of Public Comment Period on the CONTINUE convention

[William Pence]

On 3/11/2016 10:51 AM, Tom McGlynn (NASA/GSFC Code 660.1) wrote:
>
> Paragraph 4.4.2 says that
> keywords discussed later in the standard are optional but must be used
> only in the way described here.  If that statement applies to CONTINUE
> values, then in the future  CONTINUE can now only be used in the
> commentary style.  However CONTINUE is defined earlier in the standard
> than 4.4.2 and I can't find an equivalent statement that definitely
> applies to it.  Still they are mentioned in the new 4.4.2.4 so maybe the
> statement applies.  By contrast, since COMMENT and HISTORY keywords are
> defined in 4.4.2.4 it is clear that 4.4.2 states that  they may not be
> used with values.

To make it clear that CONTINUE is a reserved keyword and must only be 
used as discussed here, I suggest that the first mention of the CONTINUE 
keyword, in bullet #5 in section 4.2.1.2, be modified to add a forward 
reference to section 4.4.2, as in "Write each subsequent substring, in 
order, to a series of keywords that all have the reserved keyword name 
(see 4.4.2) CONTINUE in bytes 1 through 8 ..."
>>
>>> If someone has used CONTINUE as a keyword, have their files become
>>> illegal?
>>> I don't actually care what the answer to this is, but I think it should
>>> be clarified either way.

This general issue of what happens if an older FITS files has used a 
newly reserved keyword in a different way is clearly not unique to the 
CONTINUE convention, so I suggest that this discussion be deferred for 
now.  But I will add that I do not think this is a significant issue 
because the FITS community is small enough that we will likely know if a 
proposed new keyword conflicts with any significant previous usage.  I 
know from personal experience that past FITS committees have taken great 
care to never knowingly change the definition of an existing keyword 
because of the "Once FITS always FITS" edict.  In the one notable 
exception where the definition of the DATE related keywords had to be 
changed because of the Y2K issue, explicit language was added to specify 
at what date the definition changed.

> Given that there is now no limit on the length of strings whatsoever,
> perhaps the [final sentence in 4.2.1.1] should be omitted.  Actually you could get rid of
> the entire paragraph, and start the new section with the sentence that
> notes that a single line char string can be only so long and then goes
> on to note the new capability.  I think this would flow better and make
> it seem like the long strings were an organic part of FITS rather than
> an ad hoc add on -- even if the latter is true!

Given that these sentences have been in the Standard since 1999, I don't 
think we should suddenly delete them without more deliberate review and 
consideration.

-Bill