I also didn’t find PCE in the list mentioned in XML_Implementation_Standard
Maybe that’s just a recommendation, I don’t find any unit code validation other than having to exist with a maximum of 127 characters.
<xsl:if test="exists(cbc:InvoicedQuantity/@unitCode) and string-length(cbc:InvoicedQuantity/@unitCode) > 127">
<svrl:failed-assert xmlns:svrl="http://purl.oclc.org/dsdl/svrl" location="{schxslt:location(.)}" flag="warning" id="BR-KSA-F-06-C18">
<xsl:attribute name="test">exists(cac:InvoiceLine/cbc:InvoicedQuantity/@unitCode) and string-length(cac:InvoiceLine/cbc:InvoicedQuantity/@unitCode) > 127</xsl:attribute>
<svrl:text>[BR-KSA-F-06-C18] - Field character limits for Invoiced quantity unit of measure field (BT-130) have not been met. The maximum limit is 127 characters.</svrl:text>
<svrl:message-code>BR-KSA-F-06-C18</svrl:message-code>
<svrl:message-category>Business rules - integrity constraints (BR)</svrl:message-category>
</svrl:failed-assert>
</xsl:if>