code: def each(&block)
        @reader.each do |node|
          if @reader.node_type == 1 && @reader.name == "Product"
            str = @reader.outer_xml
            if str.nil?
              yield @product_klass.new
            else
              yield @product_klass.from_xml(str)
            end
          end
        end
      end
docs: Iterate over all the products in an ONIX file