regions []userRegion

	// rangeState is the state of special time ranges bound to this goroutine.
	rangeState
}

// beginRegion starts a user region on the goroutine.
func (s *gState) beginRegion(r userRegion) error {
	s.regions = append(s.regions, r)
	return nil
}

// endRegion ends a user region on the goroutine.
func (s *gState) endRegion(r userRegion) error {