MSDN class documentation often uses "you" to refer to developers.
When you inherit from WebRequest, you must override the following members...
You do not typically inherit from ButtonBase. To create your own button class, inherit from the Button, CheckBox, or RadioButton class....
You can also simply state what the requirements are for descendent classes. It is implied that developers are your audience.
Classes that inherit IDbConnection must implement all inherited members, and typically define additional members to add provider-specific functionality.
In your example, instead of "Implementers should implement this", write "Descendent classes must override InternalExecute to..." or "In descendent classes, you must override InternalExecute to...".