Time.zone_utc?

# File tmp/rubies/ruby-3.0.5/lib/time.rb, line 95
def zone_utc?(zone)
  # * +0000
  #   In RFC 2822, +0000 indicate a time zone at Universal Time.
  #   Europe/Lisbon is "a time zone at Universal Time" in Winter.
  #   Atlantic/Reykjavik is "a time zone at Universal Time".
  #   Africa/Dakar is "a time zone at Universal Time".
  #   So +0000 is a local time such as Europe/London, etc.
  # * GMT
  #   GMT is used as a time zone abbreviation in Europe/London,
  #   Africa/Dakar, etc.
  #   So it is a local time.
  #
  # * -0000, -00:00
  #   In RFC 2822, -0000 the date-time contains no information about the
  #   local time zone.
  #   In RFC 3339, -00:00 is used for the time in UTC is known,
  #   but the offset to local time is unknown.
  #   They are not appropriate for specific time zone such as
  #   Europe/London because time zone neutral,
  #   So -00:00 and -0000 are treated as UTC.
  zone.match?(/\A(?:-00:00|-0000|-00|UTC|Z|UT)\z/i)
end