The accounts book saves information relevant to billing the order. By default these form values are included:
b_nickname b_name b_address b_city b_state b_zip b_country b_phone mv_credit_card_type mv_credit_card_exp_month mv_credit_card_exp_year mv_credit_card_info
The values are saved with the [userdb function=set_billing] tag call, and are recalled with [userdb function=get_billing].
A list of the keys available is kept in the form value accounts, suitable for iteration in an
HTML select box or in a set of links.