sub row {
  # $tab is a number.
  # $type is one of the keys from the %types table below.
  # $cells is an array ref list of the cells in the row.
  my ($tab,$type,$cells) = @_;

  my %types = (
    header => 'h',
    data   => 'd',
    whead  => 'd'
  );

  line($tab,qq(<tr>));

  # Rows which start with a header need to have the first cell 
  # shifted off to receive the th tag.
  if ($type eq 'whead') {
    my $cell = shift @{$cells};
    cell($tab + 1,'h',ucfirst $cell, { class => 'row_header' });
  }

  # Most cells do not need anything special so the contents can be passed
  # as $value, however if the cell needs formatting or other attributes,
  # it can be passed as an array ref [$contents, { ... options ... }].
  my $cell_type = $types{$type};
  for my $cell (@{$cells}) {
    if (ref($cell) eq 'ARRAY') {
      cell($tab + 1,$cell_type,$cell->[0],$cell->[1]);
    }
    else {
      cell($tab + 1,$cell_type,$cell);
    }
  }

  line($tab,q(</tr>));
}