▁not ▁the ▁other . ▁The ▁axis ▁of ▁rotation ▁is ▁usually ▁vertical . ▁In ▁some ▁cases , ▁such ▁as ▁h ing ed ▁gar age ▁doors , ▁the ▁axis ▁may ▁be ▁horizontal , ▁above ▁the ▁door ▁opening . ▁ ▁Do ors ▁can ▁be ▁h ing ed ▁so ▁that ▁the ▁axis ▁of ▁rotation ▁is ▁not ▁in ▁the ▁plane ▁of ▁the ▁door ▁to ▁reduce ▁the ▁space ▁required ▁on ▁the ▁side ▁to ▁which ▁the ▁door ▁opens . ▁This ▁requires ▁a ▁mechanism ▁so ▁that ▁the ▁axis ▁of ▁rotation ▁is ▁on ▁the ▁side ▁other ▁than ▁that ▁in ▁which ▁the ▁door ▁opens . ▁This ▁is ▁sometimes ▁the ▁case ▁in ▁trains ▁or ▁air plan es , ▁such ▁as ▁for ▁the ▁door ▁to ▁the ▁to ile t , ▁which ▁opens ▁in ward . ▁ ▁A ▁swing ▁door ▁has ▁special ▁single - action ▁h ing es ▁that ▁allow ▁it ▁to ▁open ▁either ▁out wards ▁or ▁in wards , ▁and ▁is ▁usually ▁spr ung ▁to ▁keep ▁it ▁closed . ▁ ▁French ▁doors ▁are ▁derived ▁from ▁an ▁original ▁French ▁design ▁called ▁the ▁cas ement ▁door . ▁It ▁is ▁a ▁door ▁with ▁l ites ▁where ▁all ▁or ▁some ▁pan els ▁would ▁be ▁in ▁a ▁cas ement ▁door . ▁A ▁French ▁door ▁tradition ally ▁has ▁a ▁m ould ed ▁panel ▁at ▁the ▁bottom ▁of ▁the ▁door . ▁It ▁is ▁called ▁a ▁French ▁window ▁when ▁used ▁in ▁a ▁pair ▁as ▁double - le aved ▁doors ▁with ▁large ▁glass ▁pan els ▁in ▁each ▁door ▁leaf , ▁and ▁in ▁which ▁the ▁doors ▁may ▁swing ▁out ▁( typ ically ) ▁as ▁well