/**
* Pies the last id prefix.
* Now all ids rendered by Pie_Html will be prefixed with the
* id previously on top of the stack, if any.
* @return string|null
* The prefix that has been pieped, if any
*/
static function pieIdPrefix()
{
if (count(self::$id_prefixes) <= 1) {
throw new Exception("Nothing to pie from prefix stack");
}
$pieped_prefix = array_pop(self::$id_prefixes);
self::$id_prefix = end(self::$id_prefixes);
return $pieped_prefix;
}