Re: Base

> "Here is the canonical
> address which I request to be used in retrieving the object you are now 
> reading".

Another equally valid interpretation has already been given --
"Here is the name by which I prefer to be known, even if it is not
a valid address for me."

In neither case can you be sure that two files with the same canonical
address are in fact the same, since it is maintained by humans.

I think it may give people a false sense of security, and I don't see
that it helps a robot.  I _do_ see that "here is the base against which
partial URLs should be constructed if you have to go out and fetch another
document" is useful, and if fact essential for use in environments where
documents are stored in databases, or for serving up the result of a query.

Panorama's processing instruction gives _an_ address by which the given
document might have been fetched, and that will be used for bookmarks.
It doesn't have to be in any sense canonical or blessed.