--- a/uwproj.xsd	Tue Oct 10 20:33:49 2023 +0200
+++ b/uwproj.xsd	Wed Oct 11 20:41:26 2023 +0200
@@ -212,7 +212,7 @@
             <xs:element name="value" type="OptionValueType" minOccurs="0" maxOccurs="unbounded"/>
             <xs:element name="default" type="OptionDefaultType" minOccurs="0" maxOccurs="unbounded"/>
         </xs:sequence>
-        <xs:attribute name="arg" type="xs:string"/>
+        <xs:attribute name="arg" type="xs:string" use="required"/>
     </xs:complexType>
 
     <xs:complexType name="OptionValueType">