retracts behind the fixed unit 1 in order to avoid the obvious consequences and injuries incurred in such a situation all prior art sliding door assemblies of the above description must be set up in such a manner that the sliding units are incapable of moving right across the face of the fixed units and are in fact made to stop short of such a full opening in order to specifically allow a space 7 of a fixed size to be retained even when the sliding units 2 are fully open such a provision thereby prevents any fingers or other projections being caught in the gap provided by space 7 however such a provision whilst allowing for public safety of course restricts the available opening of the space through which people and objects can pass such a restriction in its own right may not create to many difficulties however another serious problem occurs as the remainder of the sliding unit that is left projecting after the sliding panels have u201c fully opened u201d provides ample opportunity to catch objects like shopping trolleys and people by as they attempt to traverse the opening such altercations with the opened sliding units may result in not only injury to the public but also damage to the sliding units and opening mechanisms etc in order to overcome such a disadvantage the invention has provided for the first time a particular construction of the sliding units which eliminates or substantially reduces the exposed step on the lip and thereby eliminates all of the aforesaid problems of the prior art assemblies referring to fig2 a and in particular fig2 b it can be seen that the invention provides a door or it could.