on further inspection of the xml syntax, the issue is different than I wrote originally. This line
RefAttributeType="AutomationMLBaseAttributeTypeLib/refURI"/>
should be without the / in the end so that it becomes the conclusion of a start tag (only. no end tag included)
RefAttributeType="AutomationMLBaseAttributeTypeLib/refURI">
and then the existing end tag
</Attribute>
is correct.
The second Attribute tag is this way and is correct.

I think this is correct:
<ExternalInterface
Name="Manual"
ID="fccd2ffc-114e-4775-b164-3b35aeb2c5a1"
RefBaseClassPath="UaFxAddOnIC/ManualReference"
xmlns="http://www.dke.de/CAEX&quot;>
<Attribute
Name="refURI"
AttributeDataType="xs:anyURI"
RefAttributeType="AutomationMLBaseAttributeTypeLib/refURI">
<Value>file:///attachments/manual.pdf</Value>
</Attribute>
<Attribute
Name="MIMEType"
AttributeDataType="xs:string"
RefAttributeType="AutomationMLBaseAttributeTypeLib/MIMEType">
<Value>application/pdf</Value>
</Attribute>
</ExternalInterface>

I notice mantis removed my indentation in the previous Note. :-(
(but I think the syntax is correct in the note, with the "/>" changed to ">").

Both obvservations are correct and the specification needs to be fixed

I added a cross-reference to Annex I and Annex J for the missing schema references. This cross-reference need to be checked by the group.
I increased the indentation of "</Attribute>" and "<Attribute>" to match the indentation of the "<Attribute" line above "Name="
Does the line "</Attribute>" above "</ExternalInterface>" need to be moved back to match the "Attribute" lines above it?
I removed the errant "/" from the line "RefAttributeType="AutomationMLBaseAttributeTypeLib/refURI">"

Added the missing cross-references to the schema. Corrected the xml example per the request in the issue statement.

Agrees by team