code: public void registerImplicitCollection(Class<?> clazz, String fieldName, Class<?> fieldClass) {
          _xstream.addImplicitCollection(clazz, fieldName, fieldClass);
      }
docs: Register an implicit collection (a collection that shouldn't appear as a tag in the XML).
  @param clazz class containing the field (the collection in this case), required
  @param fieldName field name, required
  @param fieldClass field type, required