code: @Override
     public void tag(Annotation sentence) {
        SequenceInput<Annotation> sequenceInput = new SequenceInput<>(sentence.tokens());
        Labeling result = labeler.label(featurizer.extractSequence(sequenceInput.iterator()));
        for (int i = 0; i < sentence.tokenLength(); ) {
           if (result.getLabel(i).equals("O")) {
              i++;
           } else {
              Annotation start = sentence.tokenAt(i);
              String type = result.getLabel(i).substring(2);
              i++;
              while (i < sentence.tokenLength() && result.getLabel(i).startsWith("I-")) {
                 i++;
              }
              Annotation end = sentence.tokenAt(i - 1);
              HString span = start.union(end);
              Annotation entity = sentence.document()
                                          .annotationBuilder()
                                          .type(annotationType)
                                          .bounds(span)
                                          .createAttached();
              entity.put(annotationType.getTagAttribute(),
                         annotationType.getTagAttribute().getValueType().decode(type));
           }
        }
     }
docs: Tag labeling result.
  
  @param sentence the sentence