   Appendix II  Addresses in the Xanadu Hypertext System 

All addresses in the Xanadu hypertext system are in the form of tumblers.
Tumbler is a term invented by Project Xanadu as a pseudo abbreviation for the
ordinal "Trans-finitesimal floating point humber."  "Humber" stands for
Hoffman (Huffman?) coded number, which is a form of variable length integer.
In appearance, a tumbler looks much like the military document numbering
system, that is used in manuals and other similarly unreadable documents.
The Xanadu hypertext system was not designed with the intent of having the end
user being aware of any addresses.  Tumblers are for the front-end program to
use in requests to the back-end. 

A tumbler is broken up like this: 

    tumbler ==> field . 0 . field . 0 . field ... 

    field   ==> integer . integer . integer ... 

Each field in a tumbler represents a different level of entity in the system. 
From left to right, the fields represent 

      which node on the network,
 
      which account/author on the node,
 
      which document by that account/author, and
 
      which region of the document; 

this field is broken up as 1.<character address> and 2.<link id>. 

The last field of the address is referred to as the v-address, the address
that is local to the specified document. 

Links have still another field which specifies the item in the link.  The
first integer of this field indicates which end of the link.  These are: 
1.<from set>, 2.<to set>, and 3.<three set>. 

The from and to sets are the meat of the link, specifying what the link
connects together.  The three set is used to define the link's type. 

In the case of a link id like 1.0.23.0.17.0.2.1 (node 1, account 23, document
 17, link 1), more fields may be put on to identify where in the link, as in 
1.0.23.0.17.0.2.1.0.1.1 (see above, fromset, first thing) 
