JSESSIONID mandatory name only in cookies not in url rewriting

Why is it that for session tracking with cookies the cookie name must be JSESSIONID whereas in url rewriting the string appended for eg in tomcat ;jsessionid is vendor dependent?

"jsessionid" is also mandatory for url rewriting. It is not vendor specific.

But Headfirst says its vendor specific and its not there in errata

From the specification :

SRV.7.1.3 URL Rewriting
URL rewriting is the lowest common denominator of session tracking. When a
client will not accept a cookie, URL rewriting may be used by the server as the basis for session tracking. URL rewriting involves adding data, a session ID, to the URL path that is interpreted by the container to associate the request with a session. The session ID must be encoded as a path parameter in the URL string. The name of the parameter must be jsessionid. Here is an example of a URL containing encoded path information: http://www.myserver.com/catalog/index.html;jsessionid=1234

So I guess,I am more inputs to be added to errata of HFSJ