| ⇢ | A | WPInv_Meta_Box_Form_Items added |
| ⇢ | C | WPInv_Meta_Box_Form_Items::output() added | |
| ⇢ | B | WPInv_Meta_Box_Form_Items::output_options() added | |
| ⇢ | A | WPInv_Meta_Box_Details::payment_form() added | |
| ⇢ | A | WPInv_Meta_Box_Form_Items::save() added | |
| ⇢ | A | WPInv_Meta_Box_Details::payment_form_items() added |