In a pre SVN 1.5 world (or if you host your repo on Dreamhost, Grr.) your externals looked thusly
And that was ok, but if you switched SVN repo hosts (like we did, moved to Assembla), it all went to hell. But now you can now use relative paths!
^/Externals/Castle castle
They swapped the order around, apparently for fun, and the ^ is the new “Root of this repo” character. It seems like ~ would have been more logical, but whatever. It’s a small change, but it makes things much easier when swapping hosts for your repo.