The file RELEASE_URL in this directory is used by the rsync infrastructure at macports to control the tag from which "released" code is provided, ultimately, at rsync://rsync.darwinports.org/dpupdate1/base. The script handling that operation checks out from svn the code tagged by the contents of the RELEASE_URL file, and makes that code available via rsync. The script is at /base/portmgr/mprsyncup.