From Xojo Documentation
Used to indicate the most mid-level scope for a members of classes and modules. Protected members can only be accessed from outside the class or module in specific situations.
In Modules, Protected means that you have to prefix the name with the module name when used outside the Module. For example a Protected property would be referred to by:
In Classes, Protected means that the item can be used in itself or its subclasses.
You do not directly use this keyword in your Xojo code. You set scope in the Inspector for the item.