This is correct.. but you'll find difference of opinions, i work for chartered architects and they all say different, i'm doing a church in newbury in September, and the architect states following expansion strips in line with the ones in the screed, with an 8mm expansion abutment at the perimeters, and then i'm working for an chartered architect in Kingston on a new build, and he states that ditra alleviates the need for expansion joints, note: they are both chartered ( which should mean the same standard )
rule of thumb: If there are expansion joints in the screed, follow then on the tile surface. full stop, if not, expansion on the tile surface only, will do nothing, or play safe and use expansion every 5m linear or through doorways with ditra. in a domestic instance, expansion joints look unsightly, in a commercial instance, it is a grey purchase, ie: its what has to be because the architect spec'd it.