plugins in parser pass variable

i have found the solution.
public static function foo(array $param) : string
return sprintf("{%s}", $param['bar']) ;
}
   
    public static function btnRead(array $arg=NULL)tring
    {
        return $arg['path'] . '{'. $arg['file'].'}.docx';
        return json_encode($arg);
    }


    public static function btnRead(array $arg=NULL):string
    {
        return $arg['path'] . '{'. $arg['file'].'}.docx';
        return json_encode($arg);