title: Hiding the PromptChar for .NET's MaskedTextBox
body: <p>Is there a way to use MaskedTextBox without displaying the PromptChar?  I would like to specify a mask to validate input against, but I don't want any prompt characters to take up space during edit mode.</p>
  
  <p>The reason for this is when I want to accept free text with a limited character set, all characters are optional alphanumerics. The problem I have is that when I select all text, even the prompt characters are selected.</p>
  
  <p>Setting PromptChar to  (" ") doesn't work.  Setting it to Zero-width space (\u200B) seems to work, but weird things happen when the mask reaches a certain length (13 characters seems to be the magic number).  Or would it be best to just roll my own?</p>