title: DateTime modify string for first day of current year
body: <p>im looking for the DateTime modify String for the first day of the year (now 1. January 2011). I tried the following:</p>
  
  <pre><code>&lt;?php
  
  $time = new DateTime();
  
  // works as expected, the first day of the current month
  $time-&gt;modify('first day of this month');
  echo $time-&gt;format('c')."\n";
  
  
  // this doesn't work. I also tried several other ways
  $time-&gt;modify('first day of january');
  echo $time-&gt;format('c')."\n";
  
  &gt;
  </code></pre>
  
  <p>I know there are other ways to retrieve the date, but I search an string for DateTime->modify() no other solution. </p>