[nightpool]

how is "%%@~" different from, say, "°"? Since they're both designed to be contentless, couldn't you form a bijection between them without losing anything? (And if your objection is atomicity, how do you feel about "%" and "°"?)

[endgame]

The premise here is wrong, because lens operators are very much designed to carry meaning. See my sibling comment (parent->parent->sibling, I guess), but operators with `@` operate on indexed optics, and the leading `%%` means "modify, and collect summary".