I think it's called when defining the options dynamically the first time. When calling for example:
```
MongoDBMapping mapping = ...
		mapping
			.entity( ExampleForMongoDBMapping.class )
				.property( "content", ElementType.FIELD )
					.associationStorage( AssociationStorage.COLLECTION );
```
It will be called when calling the "entity".
So it should be called on startup when scanning the enityt classes.
I will check this, anyway.