@Override
    public Set<Class<? extends OptimizationStrategy>> applyPrior() {
        return PRIORS;
    }
Ranks the given step. Steps with lower ranks can be moved in front of steps with higher ranks. 0 means that
the step has no rank and thus is not exchangeable with its neighbors.

@param step the step to get a ranking for
@return The rank of the given step.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/strategy/optimization/FilterRankingStrategy.java