Hey Ozz!

 ON> ISO and RFC state not to use +0000, should use "Z" to avoid
 ON> RgeExpr errors.

I am not sure I follow.  Here are three examples I have for --iso-8601,
--rfc-email and --rfc-3339 using coreutils's date app on linux;

date --iso-8601=seconds; 2019-03-10T00:47:36+00:00
date --rfc-email; Sun, 10 Mar 2019 00:47:36 +0000
date --rfc-3339=seconds; 2019-03-10 00:47:36+00:00

Note that all have the + character which I believe is correct for UTC. 
Personally I'd avoid --rfc-email given the output string is in English.  All
three formats convert fine to PST8PDT;

TZ=PST8PDT date --date="2019-03-10T00:47:36+00:00"; Sat Mar  9 16:47:36 PST
2019
TZ=PST8PDT date --date="Sun, 10 Mar 2019 00:47:36 +0000"; Sat Mar  9 16:47:36
PST 2019
TZ=PST8PDT date --date="2019-03-10 00:47:36+00:00"; Sat Mar  9 16:47:36 PST
2019

For purely %Z as per strftime() output this works;

date +%Z; UTC

For the record I still maintain that +00:00 or +0000 or even +00 is not a
number.  It is a string.  Some people, no names mentioned (mark lewis), seem to
 be misguided into believing that it is a number.

 ON> Nice to note another person contributing answer(s) instead of
 ON> arguing to argue

Aw.  You're no fun anymore.

Life is good,
Maurice

... Don't cry for me I have vi.
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 * Origin: Little Mikey's EuroPoint - Ladysmith BC, Canada (2:280/464.113)