Conditional validation of many fields

[alexliz]

I have toiled but I keep getting cornered. So...

Is there a way to conditionally validate, say, field A, so that if field B is blank, then A must be blank as well; and if A is not blank, then also B must contain some data?

Conversely, suppose A and B contain some data already, as per validation rules. Then if I delete A, B must warn me that it must now be empty, too!

Any help most welcome and thanks in advance.