在html标记中删除了空格

My current problem is with JBBCode library. When I use tag ( I know it is depreceated ), my tag with parameter become where x is the size.

My code :

 $font_size = '<font size="{option}">{param}</font>';
        $builder = new CodeDefinitionBuilder('size', $font_size);
        $builder->setUseOption(true)->setOptionValidator(new \JBBCode\validators\CssColorValidator());
        $this->definitions[] = $builder->build();

The result :

So how can I force a whitespace in the tag ?