code: func IsZoneKnown(t time.Time) bool {
  	if t.Location() == UnknownLocation {
  		return false
  	}
  	if _, off := t.Zone(); off == -60 {
  		return false
  	}
  	return true
  }
docs: // IsZoneKnown reports whether t is in a known timezone.
  // Perkeep uses the magic timezone offset of 1 minute west of UTC
  // to mean that the timezone wasn't known.