I would like to display the different section names in the header. There is a callback function but how do I implement it in koolreport?

This is my code in the export.php:

"header"=>array(
            "height"=>"30px",
            "contents"=> array(
                'callback'=>'function (pageNum, numPages) {
                    return "<p>Page " + pageNum + " of " + numPages + "</p>"; //WORKS fine
                }'
            ),
        ),

I've also tried the following, which only returns the string.

"contents" => 'phantom.callback(function (pageNum, numPages) {
                    return "<p>Page " + pageNum + " of " + numPages + "</p>"; 
                })'

I found this post:

https://stackoverflow.com/questions/17102287/footers-contents-dont-seem-to-work

But how does it fit in to KoolReport? That would great possibility to customize the report.