Confusing explanation of index vs id in the docs

[piotr-dobrogost]

At https://libtmux.git-pull.com/about.html one reads the following

What is a {pane,window}_index vs a {pane,window,session}_id?
Pane index refers to the order of a pane on the screen.
Window index refers to the # of the window in the session.

It is hard to read.
The first thing is I took {x,y} automatically to mean a pair and {x,y,z} to mean a triple.
The second thing is you mention _index vs _id and then you refer to both with index? After reading this I still do not now which is which.