Note that effects cannot be applied to groups, the objects must be specified explicit.
Is this correct? In $FGDATA/Docs/README.effects that limitation is missing.
I assume "groups" means groups in the object hierarchy, i.e. a group is an object that has children ("sub" objects). For testing I applied an effect to a group (an object that has child objects) and it seems to work. The sub objects were also displayed by the effect applied to the parent. So, as far as I can see, effects can be applied to groups. Or do I miss something?