In step 1, we used MultiLayerNetwork for demonstration purposes. For MultiLayerNetwork, featurizeExtractionLayer refers to the layer number (integer). For ComputationGraph, featurizeExtractionLayer refers to the layer name (String). By shifting frozen layer management to the transfer learning builder, it can be grouped along with all the other transfer learning functions, such as fine-tuning. This gives better modularization. However, the transfer learning helper has its own advantages, as we discussed in the previous recipe.