title: Best practice for handling vertical tabs and other invalid xml characters
body: <p>I have an application which (like many others) takes in user input, stores it in a database and then later processes it using (amongst other things) XML tools. The application takes in free text input and like many other developers I am very careful with escaping and quoting so it can handle input containing different types of whitespace, quote characters, reserved XML characters etc.</p>
  
  <p>However, occasionally a user will manage to enter a string containing a vertical tab character (hex 0B) or a form feed (hex 0C). this cannot be processed by XML tools at all and causes the app to barf.</p>
  
  <p>In my application it's quite important to preserve the original input during the 'round trip' process, so i'm loath to just strip out any characters I don't like, especially things like form feed which are still occasionally used in plain text files.</p>
  
  <p>is there any accepted best practice or general strategy for handling these characters when XML processing is involved?</p>