public function insertAfter($indexitem, $item)
{
if ($this->getReadOnly()) {
throw new TInvalidOperationException('list_readonly', get_class($this));
}
if (($priority = $this->priorityOf($indexitem, true)) === false) {
throw new TInvalidDataValueException('list_item_inexistent');
}
$this->insertAtIndexInPriority($item, $priority[1] + 1, $priority[0]);
return $priority[2] + 1;
}