This probably isn't what you want to learn, but with HTML::Tree (and HTML::Element) it's easy (though this is untested pseudo-code)

use strict;
use HTML::Tree;

my $tree = HTML::Tree->new_from_content($html_from_lwp);
my $description = $tree->look_down( "_tag", "div", "class", "text12");
+  
my $trimmed_text = $description->as_text();
[download]

This assumes that you want the first <div> where class = text12.