How to print detail data in page header and have it change for each page

I have a requirement to generate a document for a sales order that places items with different size category attribute on different pages.  I think I have the grouping issue figured out (maybe??).
But I need to indicate at the top of the page the product size for the items on the page.  Can I set a header value based upon a detail record value and reset for each page??

Thanks,

Scott


PS:  Basic XML data structure is
<order>
  <order_number> </order_number>
  ........
  <line>
    <item_number></item_number>
    <product_size></product_size>
   ........
  </line>
</order>