protected override void OnDetaching()
        {
            Masking.SetMask(attachedTextBox, null);
            attachedTextBox = null;

            base.OnDetaching();
        }
        private void AttachTextBox(TextBox textBox)
        {
            attachedTextBox = textBox;

            Masking.SetMask(attachedTextBox, @"^[a-zA-Z][a-zA-Z0-9\._-]*$");
        }