how to add a text on the .xsl style sheet

Need to add some more text at the bottom of the .xsl sheet associated with the PO layout.

already downloaded the .xls from template files region of the XML publisher.

Templated> view template: Standard Purchase Order Stylesheet with Logo

File name

XX_PROD_PO_STANDARD_XSLFO31.xsl

stuck here to modify this file.

Q1. where to add the extra text

appreciate if there is a whitepaper or doc to assist us.

rgds