Add progressive LogicItem #20
Description
Minimally, this could be a subclass with data consisting of a term for the progressive group, and a list of items. The effect of the item would be to use the term to index the list to select an item to give (empty if the index is out of bounds) and to subsequently increment the term.
A richer implementation, allowing multiplicity and for items to choose their predecessors consistent with a partial ordering on the progressive group, could instead be based on the reference code at ProgressionItemGroupModule. This implementation would instead require one term per unique item, to count collected instances. I think this would be strongly preferred over the minimal implementation.
It's not clear that any reasonable notation could be adopted to incorporate this into item strings as a first-class operation. However, it is possible to express as a StringItem consisting of nested conditionals into reference expressions, so perhaps there could be a utility method to build such an item string.