Navigation tour
The sidebar is an elevator through the knowledge tree. Each floor is one level deeper, and you always know which floor you are on. Pick a floor, or let it descend.
Click a floor to jump there.
L0
The whole library is one tree. The top level is the set of tracks, so your first choice is simply the area you want: offense, defense, governance and the rest.
A single tree mirrors how security knowledge actually nests, from broad fields down to one precise technique.
The breadcrumb is your floor indicator. At any depth you can see the full path back to the ground floor.
Every level keeps its neighbours in view, so you compare options and move sideways, not just down.
Search is the express elevator: type a page and go straight to its floor.
The tree is identical across locales, so switching language never moves the floors.
Every floor has its own URL, so a link drops someone on the exact page, at the exact depth.