@Override
      public ContentHandlerWithResult<T> create() {
        try {
          return ctor.newInstance();
        } catch (Exception e) {
          throw new IllegalArgumentException("exception attempting to instantiate " + ctor, e);
        }
      }
Will call {@link ContentHandlerWithResult.Factory#create()} on {@code handler} for each
content stream. The {@code handler} is expected to have a generic parameter of {@code type}.
sax/src/main/java/feign/sax/SAXDecoder.java