Rigour in the STEP exam

Hello, in regards to the STEP exam, I was wondering, for a full mark question, to what degree of rigour does one need to write their workings? Does it have to be as clear as something from the Elements, or can it follow the brevity seen in a mark scheme answer in an A level paper? For example, if the reason you have done some working is clear at A level, but you do not explicitly write it down, you run the risk of being docked marks, is this the same in the STEP exams?