title: RegularExpressionValidator syntax for multiline TextBox?
body: <p>I have a multiline <strong>TextBox</strong> for which any of the following inputs are valid:</p>
  
  <ol>
  <li>Empty string (the text can optionally be blank upon submit).</li>
  <li>A single numeric (0 - 9) string, up to 9 digits long.</li>
  <li>Multiple numeric strings, each up to 9 digits long, each separated by carriage return (\r) and/or newline (\n).</li>
  </ol>
  
  <p>What regular expression will enable me to validate these criteria, using a <strong>RegularExpressionValidator</strong> control? I'm currently experimenting with the excellent <a href="http://www.ultrapico.com/Expresso.htm" rel="nofollow">Expresso</a> tool, but would appreciate insight in evaluating these multiple criteria efficiently at once. </p>