def getItemsById(authorized_groups, unrestricted, itemIdentifiers):
    """
        Get items by item id.

        Each item in the returned list is a unicode string that
        represent the XML of the item as it was published, including the
        item wrapper with item id.

        @param authorized_groups: we want to get items that these groups can access
        @param unrestricted: if true, don't check permissions
        @param itemIdentifiers: C{list} of item ids.
        @return: deferred that fires a C{list} of (item, access_model, id)
        if unrestricted is True, else a C{list} of items.
        """
