public static WithOptionsVisitor instance() {
        if (instance == null) {
            instance = new WithOptionsVisitor();
        }
        return instance;
    }
Covers {@code String} oriented constants used as arguments to {@link GraphTraversal#with(String)} steps.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/WithOptionsVisitor.java