What is the purpose of the NamespaceSupported element?

The entire description of the NamespaceSupported element currently consists 
of:

'The NamespaceSupported element identifies any namespace extensions supported by 
the messaging service implementation. 
Examples are Security Services Markup Language[S2ML] and Transaction Authority Markup Language[XAML]. For 
example, support for the S2ML namespace 
would be defined as follows:

<NamespaceSupported location = "http://www.s2ml.org/s2ml.xsd" version = 
"0.8">http://www.s2ml.org/s2ml</NamespaceSupported>'

I find the above description rather obscure. It 
is not clear to me how an implementation would actually makes use of this 
information. The Messaging Service spec does not refer to any such concept 
defined in the CPA.

The example in Appendix A shows:

<tp:NamespaceSupported tp:location = "http://ebxml.org/project_teams/transport/messageService.xsd" 
tp:version="0.98b">http://www.ebxml.org/namespaces/messageService</tp:NamespaceSupported>

<tp:NamespaceSupported tp:location = "http://ebxml.org/project_teams/transport/xmldsig-core-schema.xsd" 
tp:version="1.0">http://www.w3.org/2000/09/xmldsig</tp:NamespaceSupported>

Is the namespace http://ebxml.org/project_teams/transport/messageService.xsd explicitly 
identified to show that ebXML Messaging Service is used? Does it hurt if the 
above namespace is not explicitly identified? Similarly, must the namespace http://ebxml.org/project_teams/transport/xmldsig-core-schema.xsd be 
explicitly identified if XMLDSIG is used? Isn't it already known that the 
Messaging Service calls for the use of XMLDSIG for sigining purposes?

Thanks,

-Arvola