docs: def current_spi_to_number(self):
          """
      Convert subpage & subitem to a integer
  
      * if page == 1, then return 0, since the item count is the true # of items
      * if page == 2, then return, page-1 * items_per_page, since we are
        returning the # of items on a full page.
  
      Args:
          * None
  
      Returns:
          * Integer - Which represents the number of items up to the page.
          """
          if self.slots['subpage'] == None:
              return self.sub_pi_to_number(0, 0)
          else:
              return self.sub_pi_to_number(self.slots['subpage'],
                                           self.slots['subitem'])