title: Does RegularExpressionValidator use other flavor than Regex?
body: <p>I want to do preliminary check if entered string looks like <a href="http://en.wikipedia.org/wiki/Vehicle_identification_number" rel="noreferrer">Vehicle Identification Number (VIN)</a>. I know what it consists of 17 letters and digits, but letters I, O and Q are not allowed inside VIN, so I use this regular expression:</p>
  
  <pre><code>^[0-9A-Z-[IOQ]]{17}$ 
  </code></pre>
  
  <p>Now if I check a string like 1G1FP22PXS2100001 with RegularExpressionValidator it fails, but CustomValidator with this OnServerValidate event handler</p>
  
  <pre><code>Regex r = new Regex("^[0-9A-Z-[IOQ]]{17}$");
  args.IsValid = r.IsMatch(TextBox1.Text);
  </code></pre>
  
  <p>works well. </p>
  
  <p>Experiments show what RegularExpressionValidator doesn't support <a href="http://msdn.microsoft.com/en-us/library/ms994330.aspx" rel="noreferrer">Character Class Subtraction</a>, but Regex class does.</p>
  
  <p>Now I am interested why do these two .NET classes use different regex flavors? Is it documented somethere? </p>