function createExdate() {
    $cnt = count( $this->exdate );
    if( 0 >= $cnt )
      return;
    $output = null;
    foreach( $this->exdate as $theExdate ) {
      $content = $attributes = null;
      foreach( $theExdate['value'] as $eix => $exdatePart ) {
        $formatted = $this->_format_date_time( $exdatePart );
        if( isset( $theExdate['params']['TZID'] ))
          $formatted = str_replace( 'Z', '', $formatted);
        if( 0 < $eix ) {
          if( isset( $theExdate['value'][0]['tz'] ) &&
            ( ctype_digit( substr( $theExdate['value'][0]['tz'], -4 )) ||
                ( 'Z' == $theExdate['value'][0]['tz'] ))) {
            if( 'Z' != substr( $formatted, -1 ))
              $formatted .= 'Z';
          }
          else
            $formatted = str_replace( 'Z', '', $formatted );
        }
        if( 0 < $eix )
          $content .= ',';
        $content .= $formatted;
      }
      $attributes .= $this->_createParams( $theExdate['params'] );
      $output .= $this->_createElement( 'EXDATE', $attributes, $content );
    }
    return $output;
  }