http://blogs.conary.com/index.php/smithj/2006/06/09/recipe_cleanup <-- most of the info is on the blog post. I'll list a few comments below on other (more recently added) class variables that can be used to alter the behaviour of the class. note that if you need to use the srpm url directly, it will be stored as the class variable "srpm" (called as r.srpm from within a method).
externalArchive (string) can be set if you want to pull patches and/or sources from the rpm, but want the upstream tarball to come from elsewhere
tarballName (string) used if rpmpackage can't guess the corrct tarball name contained within the rpm
distroVersion (string) the version of RHEL or Fedora Core to use to pull the rpm from. defaults to 'development' for Fedora Core or '4' for RHEL
rpmRelease (string) rpm release string (whatever's after the dash and before the dot)
isRHEL (boolean) whether to pull from the RHEL sources or not (fedora if not)
rpmPatches (list of strings) patches to apply from the rpm
rpmSources (list of strings) sources to add from the rpm
rpmUpVer (string) the upstream version of the Fedora/RHEL package. defaults to the recipe's upstream version
rpmName (string) the name of the Fedora/RHEL package, defaults to the recipe's upstream name