Setting Properties 
The application supplies a context and processes the function using a mode of operation.
Open the application in the Object Manager panel.
Under the Detail section, under the Properties tab, choose the mode of operation in the Mode field.
There are three modes of operation:
Functional mode
Event mode
Functional and Event mode
Note
If you choose Functional Mode or Functional and Event Mode, a top expression has to be assigned to the function.
In the Event mode, you do not need to assign a top expression to the function.
For more information, see Modes of Operation
Enter the context class.