title: String.Format count the number of expected args
body: <p>Is it possible to count the number of expected args/params in a string for <code>String.Format()</code>? </p>
  
  <p>For example: <code>"Hello {0}. Bye {1}"</code> should return a count of 2. </p>
  
  <p>I need to display an error before the <code>string.Format()</code> throws an exception.</p>
  
  <p>Thanks for your help.</p>