I’m pretty new to Middleman, having found it after seeing the vagrant website was written with https://github.com/mitchellh/vagrant/tree/master/website
The first thing that got my attention was they (appear!) to build the extensive menu directly from the frontmatter in each page (I made this presumption because I couldn’t find how else it could be configured) although they do run quite a heavily modified MIddleman module.
So I’m wondering if it is possible to have a collection of pages, each with sidebar information in the frontmatter, and then to dynamically generate the sidebar from all of those pages. (presumably prior to the actual page generation)