What will the the classic approach is to make pairwise comparisons between the groups in edgeR?

The edge manual I understand

The classic edgeR approach is to make pairwise comparisons between the groups. For example,

et <- exactTest(y, pair=c(“A”,”B”))
will find genes differentially expressed (DE) in B vs A.

Similarly

et <- exactTest(y, pair=c(“A”,”C”))
for C vs A,

or

et <- exactTest(y, pair=c(“C”,”B”))
for B vs C.

I have a query about how to define group and their calculations.

1. et = exactTest(exp_study, pair=c(“Treatment”, “control”))
   will do calculation
   =Control/Treament

2. et = exactTest(exp_study, pair=c( “control” ,”Treatment”))
   will do calculation
   =Treament/Control

As I understand from the manual I need to define a group as 2. I am a little unsure about it

Please guide me regarding my confusion about defining group and their calculations.

Thank you!