We leverage Hugo sections to organize each software version into self-contained versions.
Once we are in a section we can use Hugo's scripting when it builds the site to look 'up' from a page to find its parent section. That parent section (e.g. docs/corda-os/4.4/_index.md) will contain a section_menu variable that is then used to tell each page in a section, which (left-side) menu to render.
Some pages are intentionally empty (e.g. /docs/corda-os/_index.md). They are placeholders only. Without any content or front-matter they are never rendered in the bread-crumb navigation.