private void Refresh()
        {
            Validators.Items.Clear();

            foreach (var selectedItem in SelectedItems)
            {
                var validatorHeader = ValidatorPicker.GetValidatorHeader(selectedItem);
                if (validatorHeader == null)
                {
                    continue;
                }

                var listBoxItem = new ListBoxItem
                {
                    Tag     = validatorHeader,
                    Content = validatorHeader.Name
                };

                Validators.Items.Add(listBoxItem);
            }
        }