code: func (t *Collection) VisitItemsAscendEx(target []byte, withValue bool,
  	visitor ItemVisitorEx) error {
  	rnl := t.rootAddRef()
  	defer t.rootDecRef(rnl)
  
  	var prevVisitItem *Item
  	var errCheckedVisitor error
  
  	checkedVisitor := func(i *Item, depth uint64) bool {
  		if prevVisitItem != nil && t.compare(prevVisitItem.Key, i.Key) > 0 {
  			errCheckedVisitor = fmt.Errorf("corrupted / out-of-order index"+
  				", key: %s vs %s, coll: %p, collName: %s, store: %p, storeFile: %v",
  				string(prevVisitItem.Key), string(i.Key), t, t.name, t.store, t.store.file)
  			return false
  		}
  		prevVisitItem = i
  		return visitor(i, depth)
  	}
  
  	_, err := t.store.visitNodes(t, rnl.root,
  		target, withValue, checkedVisitor, 0, ascendChoice)
  	if errCheckedVisitor != nil {
  		return errCheckedVisitor
  	}
  	return err
  }
docs: // Visit items greater-than-or-equal to the target key in ascending order; with depth info.