diff --git a/core/includes/common.inc b/core/includes/common.inc
index c117d43..dddbdef 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -6443,6 +6443,70 @@ function element_set_attributes(array &$element, array $map) {
 }
 
 /**
+ * Unsets a value in a nested array with variable depth.
+ *
+ * This helper function should be used when the depth of the array element you
+ * are changing may vary (that is, the number of parent keys is variable). It
+ * is primarily used for form structures and renderable arrays.
+ *
+ * Example:
+ * @code
+ * // Assume you have a 'signature' element somewhere in a form. It might be:
+ * $form['signature_settings']['signature'] = array(
+ *   '#type' => 'text_format',
+ *   '#title' => t('Signature'),
+ * );
+ * // Or, it might be further nested:
+ * $form['signature_settings']['user']['signature'] = array(
+ *   '#type' => 'text_format',
+ *   '#title' => t('Signature'),
+ * );
+ * @endcode
+ *
+ * To deal with the situation, the code needs to figure out the route to the
+ * element, given an array of parents that is either
+ * @code array('signature_settings', 'signature') @endcode in the first case or
+ * @code array('signature_settings', 'user', 'signature') @endcode in the second
+ * case.
+ *
+ * Without this helper function the only way to unset the signature element in 
+ * one line would be using eval(), which should be avoided:
+ * @code
+ * // Do not do this! Avoid eval().
+ * eval('unset($form[\'' . implode("']['", $parents) . '\']);');
+ * @endcode
+ *
+ * Instead, use this helper function:
+ * @code
+ * drupal_array_unset_nested_value($form, $parents, $element);
+ * @endcode
+ *
+ * However if the number of array parent keys is static, the value should always
+ * be set directly rather than calling this function. For instance, for the
+ * first example we could just do:
+ * @code
+ * unset($form['signature_settings']['signature']);
+ * @endcode
+ *
+ * @param $array
+ *   A reference to the array to modify.
+ * @param $parents
+ *   An array of parent keys, starting with the outermost key and including the
+ *   key to be unset.
+ *
+ * @see drupal_array_set_nested_value()
+ * @see drupal_array_get_nested_value()
+ */
+function drupal_array_unset_nested_value(array &$array, array $parents) {
+  $ref = &$array;
+  $unset_key = array_pop($parents);
+  foreach ($parents as $parent) {
+    $ref = &$ref[$parent];
+  }
+  unset($ref[$unset_key]);
+}
+
+/**
  * Sets a value in a nested array with variable depth.
  *
  * This helper function should be used when the depth of the array element you
@@ -6500,6 +6564,7 @@ function element_set_attributes(array &$element, array $map) {
  *   FALSE, PHP throws an error if trying to add into a value that is not an
  *   array. Defaults to FALSE.
  *
+ * @see drupal_array_unset_nested_value()
  * @see drupal_array_get_nested_value()
  */
 function drupal_array_set_nested_value(array &$array, array $parents, $value, $force = FALSE) {
@@ -6569,6 +6634,7 @@ function drupal_array_set_nested_value(array &$array, array $parents, $value, $f
  *   is returned.
  *
  * @see drupal_array_set_nested_value()
+ * @see drupal_array_unset_nested_value()
  */
 function &drupal_array_get_nested_value(array &$array, array $parents, &$key_exists = NULL) {
   $ref = &$array;