Thank you, JSKelly thomas-schaefer-nh aleksandr
The built-in TOC is a nice feature. I've used SIDSETOC to move it to the sidebar.
I'd also like to have the sidebar show a subset of all pages within a namespace. I'd prefer not to do the grouping by adding namespaces. That would be one solution, add sub-level namespaces, and then use NSPAGES.
My preferred method would use Tag and Topic, if only there were a way to pass the tag from the main page to the sidebar page.
Variants and Condition look interesting, but not what I seek.
Looks as if currently the sidebar can have access to information about the current user, but not information on its current main page. That's okay. I'll just put that cross-reference to related pages on the main page itself. Thanks!