function createTrigger() {
    $cnt = count( $this->trigger );
    if( 0 >= $cnt )
      return;
    $content = $attributes = null;
    if( isset( $this->trigger['value']['year'] )   &&
        isset( $this->trigger['value']['month'] )  &&
        isset( $this->trigger['value']['day'] ))
      $content      .= $this->_format_date_time( $this->trigger['value'] );
    else {
      if( TRUE !== $this->trigger['value']['relatedstart'] )
        $attributes .= $this->intAttrDelimiter.'RELATED=END';
      if( $this->trigger['value']['before'] )
        $content    .= '-';
      $content      .= $this->_format_duration( $this->trigger['value'] );
    }
    $attributes     .= $this->_createParams( $this->trigger['params'] );
    return $this->_createElement( 'TRIGGER', $attributes, $content );
  }