Are configuration options passable to backup-config.xml for retention rules?

Perusing http://confluence.jetbrains.com/display/TCD7/Creating+Backup+from+TeamCity+Web+UI I did not see a configuration directive for how many backups are kept.
Or would JetBrains just reccomend a build agent job to remove older backups?

Thanks, I wasn't able to find this in the forum search :(

-Jeremy