void NumericUpDown_ValueChanged(object sender, EventArgs e)
        {
            if (sender is NumericUpDown num &&
                num.Tag is TreeNode parentNode &&
                parentNode.Tag is SimpleRequirement req &&
                req.GetKey()?.Repeatable == true)
            {
                myMementos[myRequirement].Add(myRequirement.CreateMemento());
                req.myRepeatCount = (uint)num.Value;

                SaveManager.Dirty = true;
            }
        }