WIP: added text allowing "Z" for timezone offset.

[ChrisBarker-NOAA]

See issue #584 for discussion of these changes.

NOTE: I think there's consensus about allowing "Z" as a timezone offset (already allowed by udunits)

It was decided to include a "proper" recommendation that a zero or Z be included for UTC times -- but some text was added saying it is a good idea in some cases.

Release checklist

** Will do this once we've all agreed **

• Authors updated in cf-conventions.adoc? Add in two places: on line 3 and under .Additional Authors in About the authors.
• Next version in cf-conventions.adoc up to date? Versioning inspired by SemVer.
• history.adoc up to date?
• Conformance document up to date? -- no changes

For maintainers

After the merge remember to delete the source branch.
Tags are set at the conclusion of the annual meeting; until then, main always is a draft for the next version.

[ChrisBarker-NOAA]

I think I've addressed everything.

[davidhassell]

Edit - just seen the above conversion on this, so I retract the comment!

I found that the lack of space before Z is required: "If the time is in UTCm add a Z directly after the time without a space." (https://en.wikipedia.org/wiki/ISO_8601#Coordinated_Universal_Time_(UTC))

[ChrisBarker-NOAA]

OK -- I think this is in good shape.

But I'm not sure what to do about:

• Next version in cf-conventions.adoc up to date?

• history.adoc up to date?

Also: I finally found a way to look at the rendered doc. Using "Z" as the placeholder, while also allowing the string "Z" is a bit confusing:

"or the letter "Z" are allowed in Z, not time zone names or acronyms."

the second Z is bold in the html, but a bit subtle.

I'm not going to change that now, but maybe in the future?

[JonathanGregory]

Thanks, Chris.

We don't need a change to the conventions doc for this PR, so "N/A" or equivalent.

The issue should be added to the list for the working version in the revision history - however, the heading is not there. I think we first need a new working version to be created for CF 1.13, before this PR can be merged into it. David intends to do that.