public static void configureMultiLabelProvider() {
        if (STEP_TO_ARITY_FUNCTION_MAP.containsKey(LabelStep.class.getSimpleName())) {
            STEP_TO_ARITY_FUNCTION_MAP.remove(LabelStep.class.getSimpleName());
        }
        STEP_TO_ARITY_FUNCTION_MAP.put(LabelStep.class.getSimpleName(), ((Step) -> Arity.MULTI));
    }
This enum value tells that the output arity of the step is multiple.
For example: out(), in() unfold etc.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/strategy/util/StepOutputArityPredictor.java