public static int indexPartOf(String name) {
        int i = name.indexOf(":");
        return i < 0 ? 0 : Integer.parseInt(name.substring(i + 1));
    }
This return the output index part. Indexes are used for nodes with
multiple outputs.
model-integration/src/main/java/ai/vespa/rankingexpression/importer/operations/IntermediateOperation.java