Another weird question. Today I was looking through the Calibre manual online for a way to create a list of books found in a search as a text document (to hunt thrift stores for books I'm missing in a series), and stumbled over the idea of hierarchical lists. I jumped on the idea of doing sub-series!
But now I'm looking for collection support. Ideally, my books should appear BOTH in the main series collection and the "Main.Sub" collection. Of course, it only puts them in main.sub at the moment. Don't know if this requires a change of my use or the plugin, but I can't imagine I'd be the only one to want this.