in reply to Tricky regexp...

Here is a very generic example of HTML::Parser applied to your problem. replace $html with your HTML, and s///g with your pattern replacement and you should be on your way. 
#!/usr/bin/perl -w
use strict;
use HTML::Parser;

my $html = "<HTML> from a file or wherever</HTML>";

my @parsed;
my $p = HTML::Parser->new(api_version=> 3,
                          handlers=> {default=>[\@parsed,"event,text"]
+},
                         );
$p->parse($html);

for (@parsed) {
    $_->[1] =~ s///g if $_->[0] eq 'text';
}

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