Query regarding <soap:address>

Hi,
As per the section 3.8 of WSDL 1.1 specification, the soap:address can be
present as ..
<definitions .... >
    <port .... >
        <binding .... >
           <soap:address location="uri"/> 
        </binding>
    </port>
</definitions>

My doubt is that, how does the SOAP stack understand this binding element.
Since, to me this element seems to be an extensibility element. Also, as per
my current understanding extensibility elements, if present, MUST be
namespace prefixed. Correct me in case I am wrong or is the above example a
typo?

In continuation, other queries are as follows:
1> Is Binding element always required to be present, since this is the
concrete part of your message? 
2> How to interpret binding elements, as the one given in the example above?

Thanks in advance !!

Regards,
Harbhanu