Utility functions for targeting leaf-elements in a render array

I propose the following functions:

/**
 * Utility function which returns an array of references to all leaves
 * of the given render array.
 *
 * @param $render_array
 *  The array to return the leaves of.
 * @param $max_depth
 *  (Optional) Provide a positive integer here and instead of finding all leaves
 *  (i.e. elements with no children), instead all elements at this depth will be
 *  returned.
 *
 * @example
 *  // Iterate over all form elements that correspond to a field value without
 *  // caring about language or multi-valuedness.
 *  $els = cm_tools_render_array_leaves($form['my_el_name']);
 *  foreach ($els as &$el) {
 *    // . . .
 *  }
 */
function cm_tools_render_array_leaves(&$render_array, $max_depth = 0, $depth = 0) {
  $leaves = array();
  $child_keys = element_children($render_array);
  if (empty($child_keys) || (!empty($max_depth) && $depth >= $max_depth)) {
    $leaves = array(&$render_array);
  }
  else {
    foreach ($child_keys as $k) {
      $leaves = array_merge($leaves, cm_tools_render_array_leaves($render_array[$k], $max_depth, $depth + 1));
    }
  }
  return $leaves;
}

and an associated convenience wrapper:

/**
 * Returns a reference to the first leaf element from a render array (found
 * using a depth-first search).
 *
 * @param $render_array
 *  The array to return the leaf of.
 * @param $max_depth
 *  (Optional) Provide a positive integer here and instead of finding a leaf
 *  (i.e. elements with no children), instead the first element found at this
 *  depth will be returned.
 *
 * @example
 *  // Get the form element that represents a single-valued field without caring
 *  // what the language is.
 *  $el = &cm_tools_render_array_leaf($form['my_el_name'], 1);
 */
function &cm_tools_render_array_leaf(&$render_array, $max_depth = 0) {
  $all_leaves = cm_tools_render_array_leaves($render_array, $max_depth);
  if (!empty($all_leaves)) {
    return $all_leaves[0];
  }
  return NULL;
}