<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Api/etc/extension_attributes.xsd">
    <extension_attributes for="Magento\Directory\Api\Data\RegionInformationInterface">
        <attribute code="state_data" type="string[]" />
    </extension_attributes>
</config>
