Because a macro is a collection of objects, individual objects need to be specified as the macro’s input and output. This can be done in two ways: by name or by default.
If you name one object Macro-In and another Macro-Out, these will automatically become the macro’s input and output.
If there is no object named Macro-In, the upper-leftmost object becomes the macro’s input.
If there is no object named Macro-Out, the lower-rightmost object becomes the macro’s output.
Cables leading into the macro deliver events to the macro’s input object, and cables leading from the macro carry events leaving the macro’s output object.