thinsliderdoor.wad 
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Effect demonstrated: - Thin horizontally Sliding doors
a) Place a two-sided linedef on the map. It should be placed inside a sector of apropriate height(say 128 high) so that the texture tiles well. Give it a main(mid) texture which looks good for this kind of effect(say MIDBRN1).
b) Give this line a type of 442, which corresponds to a sliding Door in Lines.ddf
This is the code for the Edge prefab (if you're interested):
[442] // EDGE Sliding door (LEFT), SR + MONSTERS
TYPE=PUSH;
ACTIVATORS=PLAYER,MONSTER;
SLIDER.TYPE=LEFT;
Now when we "use" this line the door will open by sliding off to one side!
Note that in the example wad I've left a bit of a gap between the sliding door and the wall, so you can see better that it's a single unconnected line.
