I’ve come across the following statement on PeopleBooks (PeopleCode API Reference > Application Classes > When Would You Use Application Classes?). This statement can be found in PeopleBooks for PeopleTools versions 8.45 to 8.49:
In PeopleSoft application classes, instance variables are analogous to private variables in most object-oriented languages. This means that instance variables are inaccessible from PeopleCode outside the class where it is declared. I used to assume that a specific object (instance of a class) would only have access to its own instance variables. This appears not to be the case, as the following paragraphs in PeopleBooks (PeopleCode API Reference > Application Class > Self-Reference) states:
This is achieved by storing a reference to the original function, and redefining %SubmitScriptName to perform your custom logic — invoking the original function as needed.