BR-FXEXT-BR-54-2

Each Item attribute (BG-32) shall contain an Item attribute value (BT-161) or an Item attribute value with unit of measure (BT-X-12, with BT-X-12-0), but noth both.

error: the document is invalid

What the rule checks

As the rule set's publisher wrote it. The rule runs on every element the context matches, and fails where the test is false; the validator reports the line of that element.

Context
//ram:ApplicableProductCharacteristic
Test
(exists(ram:Value) and not(exists(ram:ValueMeasure))) or (not(exists(ram:Value)) and (exists(ram:ValueMeasure[@unitCode!=''])))

Checked with France Factur-X EXTENDED, Factur-X / ZUGFeRD EXTENDED