Four marks out of twenty for 'presentation' in a class 6 maths test. Marked on what?

First maths assessment paper came back today. 16 out of 20. Every answer is correct. The four marks went under 'presentation', with nothing written on the paper about what was wrong with it. His working isn't pretty but it's in order. Steps one below the other, answers underlined, margin drawn. I asked him what the teacher said and he said 'she said be neat'. That is not a criterion. Is a fixed chunk of the maths mark for neatness standard in CBSE schools now? If yes, is there a rubric I can ask to see, or do I accept that a fifth of a maths score is down to the teacher's taste?