iRPA Actions. Wait multiple. Expression

What is the Expression field in WaitMultiple Activity?

Wanted to build a recursive SAPLogon Flowchart, such that Bot would look for easyAccess, if none, look for LoginPassword Page, if none look for Logon760 Page, if none - start Logon760 - LogPass - EasyAccess.

But failed, I did not understand in the end what clauses my WaitMultiple activities generated, and how it is executed.

Also need clarifications about onError handling.