my %sc = qw ( \\* b / em _ u );
my %counts;
my %opened;

sub track  {
    $opened{$_} = 1 - ( $opened{$_} || 0 );
    return "<$sc{$_}>" if --$counts{$_} > 0 && $opened{$_};
    return "</$sc{$_}>" if ! $opened{$_};
    $_;
}

sub reg_fix  {
    my $line=shift;
    %counts = (); %opened = ();
    $line =~ s/<([^>]*<)/\&lt;$1/g; # Replace unmatched < with &lt;
    my @elems = split '(<.*?>)', $line;
    $line =~ s/<.*?>//g;
    $counts{$_} = @{[$line =~ m/$_/g]} for keys %sc;
    for my $elem ( grep !/^</, @elems )  { $elem =~ s#$_#&track#eg for keys %sc; }
    join '',@elems;
}