These appear in other places, such as the Planar Handbook, as well. You become a Cleric 7, but at level X you took an optional variant level instead of the standard core version. For all intents and purposes, you are still a cleric of your effective level, but you got different benefits for the level in question. For example, there are alternate planar levels for the druid in the Planar Handbook, to make them more appropriate to a planar campaign. It's a neat idea, as long as it isn't taken too far. It has the potential to completely dilute the core classes, but on the other hand, it allows for more customized concepts within the class. It's an interesting option.