Can indicator be used with attributes?

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Hi I have a an complex element something like this

<someValue tag="" value1="" value2=""/>

and

<someValue to="" value1="" value2=""/>

the attributes "value1" and "value2" are optional however either one of the attributes "tag" or "to" need to be present.

so can I write a xsd for the above as

<xs:complexType name="someValueType">
   <choice>
     <xs:attribute name="tag" type="xs:nonNegativeInteger" use="required"/>
     <xs:attribute name="to" type="xs:nonNegativeInteger" use="required"/>
   </choice>
   <xs:attribute name="value1" type="xs:nonNegativeInteger" use="optional"/>
   <xs:attribute name="value2" type="xs:nonNegativeInteger" use="optional"/>
</xs:complexType>