F6 not a technical doubt related to abbreviation

I would like to know in exam what extent we can use abbreviation for example in the kaplan text they have used Abbreviation like AIA for Annual investment allowance FYA for first year allowance TWDV for tax written down value my doubt is are these abbreviations allowed and i would like to know what is actually not allowed where is the line we cross for not using abbreviation its obvious we cant make our own abbreviation just a general doubt as it will make a difference in typing speed and in some cases make the completion of a paper possible or not for those with a bit of slow typing speed just because we have to think and type as fast as possible Hope you can answer this question as this will be the concern with a lot of individual facing time issues