Arbitrary page groupings

It appears that a page can be part of only one collection at this time. However, it would be good if Outline could have arbitrary page groupings, to group pages in a "set" to flip through, instead of being fixed as part of a collection. The use case is something like a series of articles as in a set of blog posts, or, pages to digest for onboarding, or, sets of knowledge that might be grouped by "basic", "intermediate" or "advanced", for example. If pages are members of a "set", the set name appears at the top of the page, and has a way to navigate previous or next, through the set, across the boundaries of a more static collection. Edit 10 Jan 2021 - Thinking about this some more, yes, you could make an onboarding set in a collection, but since you cannot have docs homed in multiple collections, it kind of leads people to copy text out of document A and paste in document B. Another alternative to all this is ju…