code: public static double getNodeTrainingProportion(Node node) {
          for (Extension extension : node.getExtensions()) {
              if (TRAINING_PROPORTION_ELEMENT.equals(extension.getName())) {
                  return Double.valueOf(extension.getValue());
              }
          }
  
          return 0;
      }
docs: Retrieves the training proportion of the given node.
  <p/>
  We represent this value in PMML as an {@link org.dmg.pmml.Extension} element of the node.
  
  @param node The {@link org.dmg.pmml.Node PMML node} for which to retrieve the training proportion.
  @return The training proportion of the given node.