sub scan ($) {
    my $line = shift;
    while ($line =~ m/<\s*(\w+)([^>]*)>/g) {
        next unless is_literal($1,$2);
        my $start   = pos($line);
        my $len     = index($line,"</$1>",$start) - $start;
        my $passage = \substr($line,$start,$len);
        $$passage   = escape_out($$passage);
        pos($line)  = $start;
    }
    print $line;
}