title: Use DatePeriod and DateInterval to get certain weekdays within a period of time
body: <p>I need to get certain weekdays within a period of time.
  Weekdays can be only one ore more, e.g. only all Mondays or all Mondays, Tuesdays and Wednesdays.</p>
  
  <p>I would like to use <a href="http://php.net/manual/de/class.dateperiod.php" rel="nofollow">DatePeriod</a> together with <a href="http://php.net/manual/de/dateinterval.createfromdatestring.php" rel="nofollow">DateInterval::createFromDateString</a></p>
  
  <p>DateInterval::createFromDateString is accepting <a href="http://php.net/manual/de/datetime.formats.relative.php" rel="nofollow">Relative Formats</a>.</p>
  
  <p>How can I pass one or more weekdays as relative formats into DateInterval::createFromDateString. Is this possible at all? </p>
  
  <p>In relative formats I can't find a format "every" that would make it possible to do</p>
  
  <pre><code>$i = DateInterval::createFromDateString('every Monday');
  </code></pre>