In addition to having stand-alone loops, you can also nest them as such (iterator variables cannot be the same):
for (var/x in 1 to 10) for (var/y in 1 to 10) ...
This forms the backbone of many things, such as working with multi-dimensional lists.
var/list/my_list for (var/i in 1 to length(my_list)) for(var/j in 1 to length(my_list)) my_list[i][j] = "[i],[j]" world << json_encode(my_list)
Try fixing the code above so it works with non-square multi-dimensional lists.