$arg = [foo=>bar=>baz=>'qux']

<SOAP-ENC:Array SOAP-ENC:arrayType="xsd:string[4]" xsi:type="SOAP-ENC:Array">
  <item xsi:type="xsd:string">foo</item>
  <item xsi:type="xsd:string">bar</item>
  <item xsi:type="xsd:string">baz</item>
  <item xsi:type="xsd:string">qux</item>
</SOAP-ENC:Array>

$arg = {foo=>bar=>baz=>'qux'}

<s-gensym3 xsi:type="namesp1:SOAPStruct">
  <foo xsi:type="xsd:string">bar</foo>
  <baz xsi:type="xsd:string">qux</baz>
</s-gensym3>