The MaskedTextBox.MaskChanged event is raised after the value of the MaskedTextBox.Mask property is changed. This event is also raised if the MaskedTextBox.MaskedTextProvider is indirectly altered by a member such as MaskedTextBox.Mask, MaskedTextBox.AllowPromptAsInput, MaskedTextBox.AsciiOnly, and MaskedTextBox.Culture.