func (l *InclusiveRanges) rangeAt(idx int) *InclusiveRange {
	if idx < 0 || idx >= l.numRanges() {
		return nil
	}
	return l.blocks[idx]
}
func (l *InclusiveRanges) rangeAt(idx int) *InclusiveRange {
	if idx < 0 || idx >= l.numRanges() {
		return nil
	}
	return l.blocks[idx]
}
// rangeAt returns the underlying InclusiveRange instance
// that was appended, at a given index