Negative density is used to subtract fog from the rest of the world.
The visible range in the slider was reduced to [-8; 8] as FogVolume
density should generally not exceed 8.0 (it can introduce aliasing).
"less" should be used for quantity, rather than "lesser".
Existing scripts that use `or_lesser` in `_get_property_list()`
will need to be updated to account for this change.
Hugo Locurcio
Yuri Roubinsky
Rémi Verschelde
clayjohn