questions about descriptions

I think I will be interested in specific descriptions and before trying to code them or whatever else, here are what I need... Mostly here to discuss on solutions to do that without "breaking" Magritte ;) - will it be good to have something like a nested descriptions (MANestedContainer ??). I have to represent event and according to the type of event (human or natural), the option list is different. How to you do that ? using a nesting container (that doesn't exist yet) or using two descriptions with maybe a MADynamic object for the second description linked to the first one... - second point, I will probably need to represent a "physical" measurement (with a unit or an intensity). Units or descriptions of intensity can be different according to what is measured. So here, what would you do ? using nested description ? What about creating a MAMeasurementDescription but if so, will it be a subclass of MAElementDescription and then MAMagnitudeDescription or will it be a subclass of MAContainer or even of MADescription ? Thanks Cédrick