title: Using invariant culture with IFormatProvider in DateTime.ParseExact
body: <p>In the First overload of ParseExact method </p>
  
  <pre><code>public static DateTime ParseExact (string s, string format, IFormatProvider provider);
  </code></pre>
  
  <p>according to Microsoft:</p>
  
  <blockquote>
    <p>If format is a custom format pattern that does not include date or time separators (such as "yyyyMMddHHmm"), use the invariant culture for the provider parameter and the widest form of each custom format specifier. For example, if you want to specify hours in the format pattern, specify the wider form, "HH", instead of the narrower form, "H".</p>
  </blockquote>
  
  <p>In particular if we use stander format pattern we could use any other cultures</p>
  
  <p>what is the really purpose of using invariant culture and widest custom specifier if we use custom format pattern that does not include date or time separators if we use?</p>