my $file = $_;
my @tags=(qw(kt bold ital ch([^>]*)));
my %allowed_tag = map { $_ => 1 } @tags;
while (defined (my $line = <F1>)) {
   $line =~ /<([^>].+)>/;
   my $tag = $1;
   die "Invalid element $tag in $.. Cannot proceed due to the above error\n"
unless exists $allowed_tag{$tag};