// static one-element cache that gives the correct
	// zone for the time when the Location was created.
	// if cacheStart <= t < cacheEnd,
	// lookup can return cacheZone.
	// The units for cacheStart and cacheEnd are seconds
	// since January 1, 1970 UTC, to match the argument
	// to lookup.
	cacheStart int64
	cacheEnd   int64
	cacheZone  *zone
}

// A zone represents a single time zone such as CET.
type zone struct {

			l.cacheStart = tx[i].when
			l.cacheEnd = omega
			l.cacheZone = &l.zone[tx[i].index]
			if i+1 < len(tx) {
				l.cacheEnd = tx[i+1].when
			} else if l.extend != "" {
				// If we're at the end of the known zone transitions,
				// try the extend string.
				if name, offset, estart, eend, isDST, ok := tzset(l.extend, l.cacheStart, sec); ok {
					l.cacheStart = estart