Display Tax & Calculation Rule description

[2cool]

How can I display the Tax & Calculation Rule description on the invoice?
Using different rules and adding their description on the invoice would be nice.

My guess it should be in prices.php or invoice_items.php but can't find it. 

should be something like:
echo vmText::_($taxDescription);
echo shopFunctionsF::getTaxNameWithValue($t->calc_rule_name,$t->calc_value);

Could someone tell me what description to use and how to embed this to the invoice.

Thanks,
Pas