As usual, after Tilmann has respneded, there's not much more to say.
However, I want to empasize on
At the moment (and there is no change in the near future) they are not supported in the new BOPF development environments like BOBX or BOPF in Eclipse anymore.
In reality, you are likely to have some information in your BO node which specifies the particular behaviour (if this varies on instance-base). E. g. you can imagine a country code which influences the execution of determinations or validations. I recommend tocode to this attribute instead of intrudicing dedicated node categories. The only caveat is that you have to implement this, ideally in the check-method of each determination. Having a common superclass implementing this check-method can easily group behaviour for a particular "category".
This solution has the benefit that you can change the category at runtime.
Cheers,
Oliver