code: func (t *Collection) VisitItemsDescendEx(target []byte, withValue bool,
  	visitor ItemVisitorEx) error {
  	rnl := t.rootAddRef()
  	defer t.rootDecRef(rnl)
  
  	_, err := t.store.visitNodes(t, rnl.root,
  		target, withValue, visitor, 0, descendChoice)
  	return err
  }
docs: // Visit items less-than the target key in descending order; with depth info.