1.3.7 Upgrade.XSL File
When upgrade.xsl is present in a form template (.xsn) file, the form server applies it to transform a form file created with an older version of the associated form template to match the latest version. Upgrade.xsl is not used when creating new form files.
When applied, the upgrade.xsl transform does the following:
Copies fields from the form file to the upgraded one.
Removes fields (3) that are no longer used.
Adds new fields (3) that have been added to the newer version of the form template.
Once the transform has been applied, the resulting form file has to be usable by the form server.