Still, perlop does describe the "e" modifier in s///e as: "Evaluate the right side as an expression", and I have to wonder whether this kind of evaluation (whatever kind it is) may have enough in common with "string eval" to have a similar effect on source filters and the Switch module. Based on evidence in the thread, it apparently does.

I think (too!) it merely makes or can make a hell to "parse", the rationale being, in any case, that one can happily use /e without feeling guilty but should do so if tempted to use /ee too.