Hi Johannes, those expressions are meant to assign to results from the event you are using or the result of an operand read.
Example #1
The ValueChanged event returns the current value of buttons enable property and is then negated for the visibility for a label.
Example #2
In this case the operand reads the name for the AlarmContent defined in a session variable. The result of that read gets assigned to the content section of the action.
Another example for displaying text in a msg box.
And a more complex example using a compound widget with custom arguments which are returned when clicked on. All arguments are assigned inside the widget and are then used to set variables defining which machine details it needs to display in the dialog that opens.
So you can see plenty of different use cases.