The Index element is this:

 

 

If you want to build an XML file with the index values, if PDF output is created, then you can add the index values directly on the text element, but if you do not want the index data to be included in the output PDF file, then you can instead add the index data via this element.

 

In the setup below a IndexRef node is added with the contents of the /Header/Reference node in the input xml file:

 

 

The resulting xml file is named the same as the PDF and contains various checksums as shown below. If you calculate the checksum yourself (again), you can verify if the contents have been altered.