title: C# Regex to match a Case Insensitive string that doesn't contain a certain string
body: <p>I want to match any string that does not contain the string "None" in any case (Case Insensitive Match),</p>
  
  <p>I referred the question <a href="https://stackoverflow.com/questions/1318279/c-sharp-regex-to-match-a-string-that-doesnt-contain-a-certain-string">C# Regex to match a string that doesn&#39;t contain a certain string?</a></p>
  
  <p>The said question gives the solution for a case sensitive, but I need to disallow the string 
  "None" in any Case.</p>
  
  <p>I need a generic regular expression for disallowing the string (Case Insensitive Match).</p>
  
  <p>For Example:</p>
  
  <ul>
  <li>NONE</li>
  <li>None</li>
  <li>NoNe</li>
  <li>none</li>
  <li>nOnE</li>
  <li>NonE</li>
  <li>nONe, etc.,</li>
  </ul>
  
  <p>Kindly assist me...</p>