Tax Exemptions DFF

Hi,

The table ZX_EXEMPTIONS is the table that stores tax exemptions (for customers for example) and according to the Oracle doc below, there are fields for DFFs but i don't find in which task these DFFs can be set: when i'm in the Tax Exemptions screen with the "Highlight Flexfield" option activated , i don't see any configurable DFF in this screen (no matter the way i access it: from Setup and Maintenance/Transaction tax/Manage Tax Exemptions or from the Tax Exemptions tab on the customer site):

Any idea where it could be set ?

Thanks