I’m not talking about that test page shown when you open the WSDL file in Internet Explorer.
I’m talking about accessing a Web Service through client-side script.
Imagine that you have a Web Forms application whose server does a Web Service operation on another server and passes the result back to the client. It serves only as a gateway between the client and the Web Service.
The feature is exposed through an HTML component (*.htc) but unfortunately it isn’t supported (anymore?) by Microsoft.