code: public function offsetExists($offset)
      {
          if (!$offset instanceof Date) {
              $offset = new Date($offset);
          }
  
          $item = $this->searchOffset($offset);
          return is_null($item) ? false : true;
      }
docs: (PHP 5 &gt;= 5.1.0)<br/>
  Whether a offset exists
  @link http://php.net/manual/en/arrayaccess.offsetexists.php
  @param mixed $offset <p>
  An offset to check for.
  </p>
  @return boolean Returns true on success or false on failure.
  </p>
  <p>
  The return value will be casted to boolean if non-boolean was returned.