(I’m away from my Roon Library and if this is possible, sorry for the mouse click 
)
I would like to reference one bookmark, say, “High School Years” (Which is a FOCUS on the original ALBUM releases during the 4 years that I was in highschool)
Next, I want to nest the Bookmark “High School Years” in the next Track FOCUS and then Filter to only “Alternative”, “Metal” and “Rock” genres. Then save a new Bookmark called “My High School Hits.”
Can this be done? Nested Bookmarks?
The next step, would be a Bookmark of the not skipped and played more than 5 times from “My High School Hits.”
A new bookmark, from the nested “My High School Hits” called “All Time Favorites.”
Not really an answer to your exact request, but you could concatenate the terms to have a list of bookmarks along the lines of:
High School Years - Alternative
High School Years - Metal
High School Years - Rock
etc.
Done that, It just makes too many bookmarks and/or I can make each bookmark and then select all to add to another bookmark.
My second post gets to the why. I would like a core set of bookmarks to be the basis for a set of dynamic bookmarks.