xslt - How can I sum up some values per page in a table in XSL-FO?

Question

I'm using XSL-FO to generate an account statement print out. The PDF is actually just a simple table with a simple header on every page. The difficulty is that I have to display transaction volumes per page, e.g.

Page 1

+------------------------------+-----------+-----------+---------------------+
| Text                         | Credit    | Debit     | Balance             |
+------------------------------+-----------+-----------+---------------------+
| Previous month               |           |           |           (*1) 1000 |
| abc                          |      1000 |           |                2000 |
| abc                          |           |       500 |                1500 |
| abc                          |           |       200 |                1300 |
| ...                          |           |           |                     |
| Carry over                   | (*2) 1000 |  (*3) 700 |           (*4) 1300 |
+------------------------------+-----------+-----------+---------------------+

Page 2

+------------------------------+-----------+-----------+---------------------+
| Text                         | Credit    | Debit     | Balance             |
+------------------------------+-----------+-----------+---------------------+
| Previous page                | (*2) 1000 |  (*3) 700 |           (*4) 1300 |
| abc                          |      1000 |           |                2300 |
| abc                          |           |       500 |                1800 |
| abc                          |           |       200 |                1600 |
| ...                          |           |           |                     |
| Carry over                   | (*2) 2000 | (*3) 1400 |           (*4) 1600 |
+------------------------------+-----------+-----------+---------------------+

Here are some explanations:

1. This is the previous month's balance. It's pre-calculated and well-known as an XSL variable. No problem with that, that's a regular header (only on the first page)
2. This value is calculated on a per-page basis. It sums up all credit amounts on the same page. I can't calculate that myself, as I don't know when XSL-FO will do the page break. So I imagine XSL-FO must do the calculation for me. The sum at the bottom of a page is the same as the value at the top of the subsequent page.
3. This value is the same as 2, only for debit amounts.
4. This value is just the last transaction's balance at the bottom of a page. That value is repeated at the top of the next page.

How can I do these calculations with XSL-FO?

See also this related question: How to display one or the other information depending on the page number in XSL-FO?

Answer 1

Try "table markers": http://www.w3.org/TR/xsl/#fo_retrieve-table-marker.

In XSLT for each row inject a marker with the sum. Then let the engine select a marker to substitute for the fo:retrieve-table-marker in table header or footer. The idea is that proper marker will be selected at rendering time depending on the marker's position on the page and @retrieve-position and @retrieve-boundary on the fo:retrieve-table-marker.