setting X11BASE

[perryh at pluto.rain.com]

After updating with portsnap, I am getting an insufficiently-helpful
error message:

    On FreeBSD before 6.2 ports system unfortunately can not set
    default X11BASE by itself so please help it a bit by setting
    X11BASE=${LOCALBASE} in make.conf.  On the other hand, if
    you do wish to use non-default X11BASE, please set variable
    USE_NONDEFAULT_X11BASE.

* Am I correct in *guessing* that "make.conf" refers to
  /etc/make.conf?

* What is the value of LOCALBASE?  I'm not finding any
  definition, or other reference, in /etc/make.conf.

* How do I figure out whether I should set USE_NONDEFAULT_X11BASE?

* Why does it even need this?  The port I am trying to install
  ATM (portmaster, to get a handle on the dependency maze) has
  nothing to do with X11.

In case it matters, I have not upgraded to the modular Xorg, and
would prefer not to go through all that.  "It ain't broke ..."