title: Regular Expression Validator to catch non-alphanumeric characters
body: <p>This is a really dense question, but I'm tired.</p>
  
  <p>I need a regular expression that can do in a validator control that will catch any non-alphanumeric characters. In other words the regexp needs to match if the string contains only a-z, A-Z or 0-9. </p>
  
  <p>I'm aware that it's quite easy to write a regular expression that will match if there's an illegal character in a string - the trouble is that I need the <em>opposite</em> of this because it's in a validator. Thats' what's giving me a headache.</p>
  
  <p>Solutions appreciated.r</p>