Altough adding descriptions would not make sense to the core, would
make sense to change MAFileModel into a MAObject? That would make it
easier to build extensions on top of it.
The idea of MAFileModel is that you can easily subclass it to provide
your own strategy to store and retrieve the file. MAFileDescription
takes the #kind: as an argument, so you can tell it what class to
Maybe you can give an example, why you need to add new values to the
existing MAFileModel subclasses?