 uses this.
        (?P<fraction>)

        # Z or [-+]hhmm
        (?:
            (?P<zulu>Z)
            |
            (?:
                (?P<dsign>[-+])
                (?P<dhour>\d{2})
                (?P<dminute>\d{2})
            )
        )
        $
    c