What does the second part of this syntax mean on the jQuery API?

I have read the method signature:

jQuery.getJSON( url, `[data,] [success(data, textStatus, jqXHR)]` )

I am wondering what the part I have highlighted in quotes means? Why does it say [data,]? Why does it have two arguments in square brackets?

Shame the jQuery site doesnt tell you how to read the documentation...

I believe it is saying the function requires the first param, the second param is optional (data), and the 3rd param is also optional, and it is a callback taking 3 parameters that is called on success

The second and third arguments are optional.

The third parameter is a function with the given parameters which are passed to it if provided.

It means the argument is optional.

It means that these are optional parameters. It's a common pseudo-coded way of representing these in documentation papers.