Many homes have a porch over the first level which is only accessible by going out and back in through a window on the second level. Would this window/doorway require a mezuzah? Is there something about a window that precludes it from being considered a door as far as hilchos mezuzah goes?
(I am ignoring all arguments about porches and access to the street in this question. Let us assume the opinion that a door in this situation would in fact require a mezuzah)