public function track($col, $msg, $level = 'normal', $merge = true) {
        if (empty($this->_row)) {
            $this->flush(); //init arrays
        }
        if (!in_array($col, $this->columns)) {
            debugging('Incorrect column:'.$col);
            return;
        }
        if ($merge) {
            if ($this->_row[$col][$level] != '') {
                $this->_row[$col][$level] .='<br />';
            }
            $this->_row[$col][$level] .= $msg;
        } else {
            $this->_row[$col][$level] = $msg;
        }
    }