1. a start tag is encountered
2. the inside text element is encountered
3. the end tag is encountered

use strict;
use warnings;
use HTML::Parser;

my $parser = HTML::Parser->new(api_version => 3);

$parser->handler(start => \&start, 'self,tagname,attr');
$parser->handler(text  => \&text,  'self,dtext');
$parser->handler(end   => \&end,   'self,tagname');

$parser->parse(q|<foo bar="qux" baz="foo">foo</foo>|);

sub start {
   my ($parser,$tag,$attr) = @_;
   print "<$tag";
   # we lose the original order of attribs, but we'll live ;)
   print qq| $_="$attr->{$_}"| for keys %$attr;
   print ">";
}

sub text {
   my ($parser,$text,$attr) = @_;
   $text =~ s/foo/bar/g;
   print "$text";
}

sub end {
   my ($parser,$tag) = @_;
   print "</$tag>";
}
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jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)