title: GetMonthName: Valid values are between 1 and 13, inclusive. Why?
body: <p>I accidentally passed 0 into <code>DateTimeFormatInfo</code>'s <code>GetMonthName</code> method:</p>
  
  <pre><code>DateTimeFormatInfo info = new DateTimeFormatInfo();
  var monthName = info.GetMonthName(0);
  </code></pre>
  
  <p>and got a <code>System.ArgumentOutOfRangeException</code> with this error message: <strong>Valid values are between 1 and 13, inclusive.</strong></p>
  
  <p>Passing in 1 through to 12 return "January" through to "December" but passing in 13 returns an empty string.  </p>
  
  <p>I can see why month numbers are not zero indexed, but what's month 13 for?  </p>