public function setFixedColumnWidths(array $columnWidths)
    {
        if ($columnWidths !== array_filter($columnWidths, 'is_numeric')
            || array_keys($columnWidths) !== array_filter(array_keys($columnWidths), 'is_int')
        ) {
            throw new \InvalidArgumentException('Array must contain integer keys and numeric values only!');
        }

        $this->columnWidths = $columnWidths + $this->columnWidths;
    }