shlishi: I didn’t mean to say that it has no mekor – the earliest mekor as far as i can remember is R’ Ahron from Belz. In the Hagodos it says to say ‘BORUCH HABA’ when you open the door. A good YEKKE like me doesn’t say such things (Seriously, it is not our minhag to say it.)
RabbiRAbin – R’ Chaim KAnievsky wrote a sefer about the things which causes one to forget his torah, which are bought all over in Halocho. It probably comes in there.
There is no question eliyahu hanavi comes to the Seder (that was never up for discussion) —:> Where is your mekor???
Commonsense – although the Gemoro clearly says isho zonah means something other than food-distributer. I heard from one of my Rebbes to reconcile the two translations: that in the olden days, a zonah would have an inn, using it to cover up for any alternative definitions.