Deciphering a Porter's Handbook paragraph

[Warren Block]

On Tue, 3 Jan 2012, Benjamin Kaduk wrote:

> I don't think we've yet said something like:
> LOCALBASE should be set to where existing ports have already been installed 
> (the ``base directory'' of where the ``local additions'' to the system have 
> been made); it is uncommon for having PREFIX != LOCALBASE in normal usage.
> We probably should say something like that.

ISWYM, but am going to delay on that for a bit to try to address the 
existing problems before adding information.

The more I looked at section 9.4, the more I wanted to rework it. 
Here is the original:
http://www.wonkity.com/~wblock/porters-handbook-orig/book.html#PORTING-PREFIX

Here is a first pass at some improvements:
http://www.wonkity.com/~wblock/porters-prefix/book.html#PORTING-PREFIX

I removed the reference to LOCALBASE sometimes being /opt.  Maybe it is, 
but that's covered under the "custom path".

There are also the references to /usr/X11R6 and imake.  Are those still 
relevant?

Then there's this:

   The variable PREFIX can be reassigned in your Makefile or in the
   user's environment.  However, it is strongly discouraged for
   individual ports to set the variable explicitly in the Makefiles.

"You absolutely should not press this big shiny button right here."
Or is that trying to say you can set PREFIX in make.conf or as an 
environment variable, but don't set it in the *port's* Makefile?
Instead:

   PREFIX should not be set explicitly in a port's Makefile.  Users
   installing the port may have reassigned PREFIX, and the port should
   respect that.