[Christopher Nelson] cites [Richard W. Stevens] as writing in his
''UNIX Network Programming'' that
   The process can let the system automatically assign a port.  For
   both the Internet domain and the XNS domain, specifying a port
   number of 0 before calling bind() requests the system to do this.

A variety of networking texts (most of them derivative of RFCs?) cite
"0-1023" as reserved port numbers, without more comment.

[CL] believes the following are true:
   * A correctly implemented stack responds to a request to use port 0 by selection of a not-currently-in-use port, generally as low as possible.
   * Tcl is "passive", that is, simply inherits the behavior of the C API over which it is implemented.
   * All recent Tcl versions for Unix and Win* behave this way for port 0 requests.
We hope someone will test out a few Tcl versions under MacOS during
October 2001.