Not a jq expert, but my understanding is:

`.[]` takes a list and turns it into a sequence consisting of each element of that list.

`| x` applies the filter `x` to that sequence, turning it into a new sequence.

The outermost `[ ]` builds a list from that new sequence.

Take each sub-item in `.` (the current item being processed), apply the function `x` to each sub-item, and collect all the result values from `x` into an array.

.map(x)

This is the most jq-ish reply xD