enable swapping position of a key=>value pair backward. ie, if applied on "swap", [0]=>bar, [1]=>foo, [2]=>swap would become [0]=>bar, [1]=>swap, [2]=>foo

array_swap_back.php

function array_swap_back($arr,$elem){
  $ndx = array_search($elem,$arr);
  $b4 = array_slice($arr,0,$ndx);
  $mid = array_reverse(array_slice($arr,$ndx,2));
  $after = array_slice($arr,$ndx + 2);

  return array_merge($b4,$mid,$after);
}