Board Game Arena

Is it stated anywhere that you can only have maximum 3 progress tokens?

THe game interface looks like it can only hold 3, but I can't find it anywher ein the rules that you can only have 3 tokens max.

Don't worry if by any chance you cumulate 4+ tokens,
the BGA 7WD interface does adapt easily (I guess it just didn't made sense to show 6 empty spaces...)