Updating DistributedArray using the primitive DArray constructor

The following syntax is demonstrated in the manual:

DArray(size(d),procs(d)) do I
...
end

I haven’t seen a loop like this before. What is I?

I is the input argument to the following do block. see https://docs.julialang.org/en/v1/manual/functions/#Do-Block-Syntax-for-Function-Arguments