On grammatical class:

fa
sumti place tag: tag 1st sumti place.
fai
sumti place tag: tag a sumti moved out of numbered place structure; used in modal conversions.
fe
sumti place tag: tag 2nd sumti place.
fi
sumti place tag: tag 3rd sumti place.
fi'a
sumti place tag: place structure number/tag question.
fo
sumti place tag: tag 4th sumti place.
fu
sumti place tag: tag 5th sumti place.

In definition:

jai
convert tense/modal (tagged) place to 1st place; 1st place moves to extra FA place (fai).