#!/usr/bin/perl

use strict;
use warnings;

while(<DATA>)
{
  chomp;

  while ( m{ <([^>]*?)> [^<]*? </\1> }gx )
  {
    my $token = $1;

    s{<$token>}{}g;
    s{</$token>}{}g;
  }

  
  # Of course, this will be hard to do if you
  # "don't know how many dashes, if any, will
  # be there."
  print "\t$_\n" for ( split (/-- /,$_) );
  print "\n";

}

__DATA__
This is a -- string of -- words
<b>This is a -- string of -- words</b>
This <b>is a -- string</b> of -- words
This <i>is</i> a -- <b>string</b> of -- words
This <i>is a -- <b>nested set</b> of</i> -- tokens
This is -- a nifty -- <A HREF="http://google.com">search engine</A>