title: Error parsing regex pattern
body: <p>I'm writing a simple regex in c# to locate backslashes not preceded or followed by any backslashes:</p>
  
  <pre><code>Regex reg = new Regex(".*(?&lt;!\\)\\(?!\\).*");
  </code></pre>
  
  <p>However, this statment generates an ArgumentException: "parsing ".(?" - Not enough )'s"</p>
  
  <p>The group parentheses seem to match.  Can anyone spot the problem?</p>