formatting - Indentation of boxes in Format.fprintf -

please consider function f:

open format  let rec f = match   | x when x <= 0 -> ()   | ->     pp_open_hovbox std_formatter 2;     printf "this line %d@." i;      f (i-1);     printf "this line %d@." i;      close_box ();     () 

it recursively opens hovboxes , prints something, followed newline hint (@.). when call f 3, obtain following output:

this line 3 line 2 line 1 line 1 line 2 line 3 

but expected:

this line 3   line 2     line 1     line 1   line 2 line 3 

can explain why obtain first output , need change obtain second one?

@. not newline hint, equivalent print_newline calls print_flush closes opened boxes , follows new line.

if want print line line format should open vertical box open_vbox , use print_cut ("@,") whenever want output new line.