Is Timestamp a security token

As far as I can understand our current definition, a <wsse:Timestamp> 
element is a security token and therefore it can occur in an embedded STR.

Put another way, the embedded reference

    <wsse:SecurityTokenReference> <wsse:Embedded>
       <wsu:Timestamp ...> ... </wsu:Timestamp>
    </wsse:Embedded> </wsse:SecurityTokenReference>

would be allowed with the same semantics as the unwrapped Timestamp element.

This might be useful if a  SOAP intermediary wants to add a timestamp that 
is different from the timestamp added by the original creator.  It could do 
so by adding an appriate usage attribute to the SecurityTokenReference.

Could someone who understands the definition of "security token" please 
confirm or deny the above.