Super Collections
From Spiffy Stores Knowledge Base
Super Collections
Notes: A Super Collection allows you to define a collection which either includes products from certain collections, or excludes products from certain collections.
Inclusion by Collection
If a product is a member of a collection that is defined as included for the Super Collection, then that product is a member of the Super Collection.
Exclusion by Collection
If a product is a member of a collection that is defined as excluded for the Super Collection, then that product is excluded from the Super Collection, if and only if it belongs to collections that have ALL been excluded.
For example, if a product belongs to 2 collections, one of which is excluded (and by definition, the other one is included), then we define the product as NOT excluded since is also belongs to an included collection. In order for a product to be excluded, then all of the collections to which it belongs must be excluded.
In practise, this is not really a restriction. Super Collections allow you to create groups of combined collections in many different ways. This means that all products should be able to be assigned to a single Custom Collection as their "natural" home.