Emacs Tidbit: rectangle-number-lines

Emacs has so many little features that do exactly what you need in very specific circumstances. Here’s one that I just found out about: rectangle-number-lines. I had some lines and I wanted to insert line-numbers for reference. I wanted this

arguments list: [
team8721038424565681034
user
fdff6f87-d876-4558-8d12-19e039e5a880
a
foo
secret
alsothis
b
e46e2d16-b3ba-4f84-826f-5e3031465e21
]

To be this

arguments list: [
 1 team8721038424565681034
 2 user
 3 fdff6f87-d876-4558-8d12-19e039e5a880
 4 a
 5 foo
 6 secret
 7 alsothis
 8 b
 9 e46e2d16-b3ba-4f84-826f-5e3031465e21
]

I started thinking about kmacros, which I rarely use but have an incrementing counter you can use for this, but I started googling and lo and behold I found a Stack Overflow post with the answer. Just highlight a rectangle on the first column¹ and type C-x r N which runs rectangle-number-lines, which does exactly what I wanted.