- Unique value of attribute
Sorry, in UML spec, the isUnique of Multiplicity is not used for Attribute.value unique or not.
If the attribute allows multiple values, Multiplicity.isUnique is used to identify its values can or not be repeatable.
(my description may confuse you, better to read the UML spec)
So, I think you may define a <<IsUnique>> stereotype for your attributes.
If you still want to use Multiplicity.isUnique, you can do it as following:
(under an attribute)
<ConditionsChecker>
<Conditions type="OR">
<ModelElementPropertyConditionChecker property="multiplicityDetail">
<Conditions>
<ValueChecker property="unique" value="true"/>
</Conditions>
</ModelElementPropertyConditionChecker>
<HasValueChecker property="multiplicityDetail" flag="false"/>
</Conditions>
<Text> [U]</Text>
</ConditionsChecker>
