Exactly. Interleaf was structured-oriented like that, only a bit moreso. (I designed "styles" heavily in all 3 tools, plus some others.)

Regarding mil/aero, I heard (possibly incorrect) that Boeing did some documentation in Interleaf, and part of routine preservation of those engineering artifacts was to archive... an entire Apollo Domain workstation network. Even though later/other versions of Interleaf were available on later platforms. I guess they weren't going to take any chances.