What is the output for this PHP for loop?

Hi guys , could somebody be kind enough to explain the output for this code. thank you very much

for($i=0; $i < 3 ; $i=$i + 1) { for ($j=0; $j < 3; $j =$j + 1) { for ($k=0;$k < 3; $k =$k + 1){ print " I: $i; J: $j; K: $k\n" ; } } }