I have in various groups a “main file” that I would like to pin at the top. I use different criteria to sort files in a group and the idea to “pin a file to the top” is to make it independent of how the others are viewed.
I use flags to mark files, that I currently work on, and need attention (with a smart rule to gather them in the sidebar) but this is not really like the idea of a pinned file. The idea is to have it placed always on top of the group in the file .
Examples for “main files”, that I like to pin to the top, are table of content files I use to navigate to files in the group, or files that contain notes or instructions about the files in that group.
Does this make any sense? … and now I worry that this exists already and I was too stupid to find it in the manual 
Thank you
Olaf