static function instance()
    {
        if ( !isset( $GLOBALS["eZHTTPToolInstance"] ) ||
             !( $GLOBALS["eZHTTPToolInstance"] instanceof eZHTTPTool ) )
        {
            $GLOBALS["eZHTTPToolInstance"] = new eZHTTPTool();
            $GLOBALS["eZHTTPToolInstance"]->createPostVarsFromImageButtons();
        }

        return $GLOBALS["eZHTTPToolInstance"];
    }