// optionally includes an additional position prior to MBB->begin(), indicated
// by the includeStart flag. This is done so that we can iterate MIs in a MBB
// in parallel with SlotIndexes, but there should be a better way to do this.
// optionally includes an additional position prior to MBB->begin(), indicated
// by the includeStart flag. This is done so that we can iterate MIs in a MBB
// in parallel with SlotIndexes, but there should be a better way to do this.