Thx Spirit, I'd Love It If Detail Caught On Oneday...
Opened the quakeforge tools source, looked in map.c for "detail" to find my answer... The detail brushes are exposed to the mapper with an "am_detail" brush entity, in the same fashion as in the Quest Ed tools ( http://quest-ed.sourceforge.net/
), as well as pOx's Mac-Carbon tools ( http://quake.chaoticbox.com/
) It's probably the same codebase. The Mac tools are especially neat because the detail entities have extra flags to make them double sided and pass-through, i.e. func_illusionaries that don't take up entity count, or not detail at all, just inert brush grouping.
This tech came out 6ish years ago and the main reason it never caught is that, even then, the neat features were bolted onto primitive compilers. The Mac version is the most improved and was actually quite nice but still had some annoying aspects like a 5120 brush limit.