I'm familiar with If .. Else in rules.
Nested If's refers to putting If conditions inside of another If condition. It would reduce a lot of rule condition duplication and would run WAY more efficiently.
Without Nested If's, every combination of conditions has to be checked independently.
IF Account.Active = True AND Account.Balance = 0 THEN
Do Action1
ELSE IF Account.Active = True AND Account.Balance > 0 THEN
Do Action2
ELSE IF Account.Active = True AND Account.Balance < 0 THEN
Do Action3
With Nest If's, if an Account is Active, the evaluation of the nested conditions continues. If an Account is not Active, the rule evaluation process stops after the first IF.
IF Account.Active = True THEN
IF Account.Balance = 0 THEN
Do Action1
ELSE IF Account.Balance > 0 THEN
Do Action2
ELSE IF Account.Balance < 0 THEN
Do Action3
