use Getopt::Long;

  my %tags = ();
  my %cmd2tags = (
   # list of cmd-line element types => correspondence to xpath (via look_down())
   'type' => '_tags',
   'class' => 'class',
   'id' => 'id',
   'name' => 'name'
  );
  GetOptions(
    "tags=s" => sub {
       # sub to be called whenever --tags XYZ is detected
       # it expects XYZ to be in the form "K=V" and K must
       # exist as a key in %cmd2tags 
       my ($k,$v) = @_;
       if( $v =~ /^(.+?)=(.+?)$/ ){ 
         my $t=$1; my $n=$2;
         my $c2t = $cmd2tags{$t};
         die "unknown tag name '$t', I know only of ".join(",", keys %cmd2tags)."\n" unless defined $c2t;
         $tags{$c2t} = $n;
       } else { die "--tags V: V must be in the form 'key=value' where key can be 'class' or 'type', e.g. ..." }
    },
    "url=s" => \$url,
 )
  or die("Error in command line arguments. $!\n");
  ...
  # now %tags contains tag-type-name=>value, e.g. '_tag' => 'div' etc.
  print "Tag received: '$_' => '".$tags{$_}."'\n" for(keys %tags);
  @results = $tree->look_down(%tags);
  ...