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