title: Why DateTime.ParseExact(String, String, IFormatProvider) need the IFormatProvider?
body: <p>If we're using the <code>ParseExact</code> method for <strong><em>exact</em></strong> date-time's parsing using a specified format, why do we need to provide a IFormatProvider object? what is the point behind it?</p>
  
  <p>For example:</p>
  
  <pre><code>DateTime.ParseExact(dateString, format, provider);
  </code></pre>
  
  <p>Why do we need the <code>provider</code> here?</p>