Either its $CLASS or $ANY the class is assigned at runtime. I'm really confused at understanding the difference.
Below is help from property rule form:
You can also enter an abstract class, or one of two keywords:
For more flexibility in activities that use this property, enter an abstract class or the keyword $CLASS. If you enter an abstract class, the activity at runtime must specify a concrete class derived from that abstract class. If you enter $CLASS, the activity must specify a concrete class (but it can be any concrete class). For example, the Code-Pega-List.pxResults property uses $CLASS.
Enter $ANY to make the class of the page (or Page Group or Page List) assignable at runtime.
Can you point to any use case where we use $ANY instead of $CLASS?