sub col {
  my ($tab,$opt) = @_;

  my @attributes;
  push @attributes, qq(class="$opt->{class}") if $opt->{class};
  push @attributes, qq(span="$opt->{span}")   if $opt->{span};

  my $format = @attributes > 0 ? ' '.join(' ',@attributes) : '';
  my $tag = 'col'.$format;
  line($tab,qq(<$tag>));
}

sub cols {
  my ($tab,$cols) = @_;
  col($tab,$_) for @{$cols};
}