/// <summary>
 /// Validates input firstName. If unsuccessful, shows the corresponding errorLabel
 /// </summary>
 /// <param name="sender"></param>
 /// <param name="e"></param>
 private void firstNameTextBox_Validating(object sender, CancelEventArgs e)
 {
     if (firstNameTextBox.Text.Length < 1)
     {
         firstNameErrorLabel.Text    = "Required";
         firstNameErrorLabel.Visible = true;
         firstNameTextBox.BackColor  = SystemColors.Control;
         return;
     }
     if (handler.IsValidFirstName(firstNameTextBox.Text))
     {
         firstNameErrorLabel.Visible = false;
         firstNameTextBox.BackColor  = SystemColors.Window;
     }
     else
     {
         firstNameErrorLabel.Visible = true;
         firstNameErrorLabel.Text    = "Invalid First name, only letters and '-' please";
         firstNameTextBox.BackColor  = SystemColors.Control;
     }
 }