Thanks I was able to copy and reuse the Java code you mentioned. Now if I use this activity in Post flow action it is a bit procedural. Above out-of-the-box skill check code is fired when save operation occurs on Operator ID instance. If I want to make my custom validation more universal than procedural, for example anytime the work object is saved it should fire, then is there any good spot to place?

With this approach, we don't need to fire validation for every flow action but implement once, and works every time work object gets saved. However, it gives validation error when user does local action without saving invalid row input and try to submit the local action. The message is irrelevant as it is an error that comes from previous screen..

Thanks,