WSDL file seems invalid, according to PHP

I’m trying to use the CSS validator programatically in a PHP script.. I’m
using PHP’s native SoapClient class. Here is my test script:

$client = new SoapClient('http://www.w3.org/2005/09/css-validator.wsdl', [
    'soap_version' => SOAP_1_2,
]);

But this gives me the following error:

SOAP-ERROR: Parsing WSDL: Couldn't find <definitions> in '
> http://www.w3.org/2005/09/css-validator.wsdl'


Is the validator using a non-standard version of SOAP?

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*Martin Bean*
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