title: Regex (.NET) - Unrecognized grouping construct
body: <p>I'm stumped on the following getting the following regex to work (VB.NET)</p>
  
  <p><strong>Input:</strong></p>
  
  <pre><code> +1.41 DS +0.93 DC x 3* @12.5 mm (4.00 Rx Calc)
  </code></pre>
  
  <p><strong>Expected Output:</strong></p>
  
  <pre><code> +0.93
  </code></pre>
  
  <p>I've gotten as far as the following expression:</p>
  
  <pre><code> DS[ \t]*[+\-][ \t]*\d{1,2}\.\d{2}
  </code></pre>
  
  <p>This returns a result of</p>
  
  <pre><code>DS +0.93
  </code></pre>
  
  <p>I need to return only +0.93 (without any leading whitespace), when i modify the Regex as:</p>
  
  <pre><code>(?DS[ \t]*)([+\-][ \t]*\d{1,2}\.\d{2})
  </code></pre>
  
  <p>I get the error unrecognized grouping construct, I don't understand why it's giving me this error. I think my non-matching group is incorrect, but i can't find why/where?</p>