package('BU:Python | versionGE(2.2)')The configure atom has the same syntax and differs from package only in inducing the correct behavior when Pacman uninstalls and updates packages. The rule that you should follow is this:
The practical effect of using configure is that packages become linked together in terms of what must be uninstalled and re-installed together.
setup('source $MYPACKAGE_LOCATION/mySetup.SHELL')which causes mySetup.csh and mySetup.sh to be sourced from the standard Pacman generated setup scripts.
register('BU','http://atlas.bu.edu/caches','Atlas Tier 2, Boston University','http://physics.bu.edu/~usatlas/','Saul Youssef', 'http://physics.bu.edu/~youssef/')defines the symbolic cache name BU, so that one can refer to BU:Python, for example.