Display column numbers on top of each column using tcpdf html

Question

Example of what I want to achieve in the image

Everything works well except that I want to display the column numbers on top of each columns. And also remember the content of each column for indexing purposes. How can I display column numbers in tcpdf documents?

        $pdf->AddPage();
        // set columns
        $pdf->setEqualColumns(3, 50);
        // print chapter body
        $pdf->selectColumn();
        // set font
        $pdf->SetFont('helvetica', '', 9);
        $pdf->SetTextColor(50, 50, 50);

        $pdf->writeHTML(stripslashes($columns), false, false, true, false, 'J');

        $pdf->Ln();