code: @Override
      public boolean onEvent(final LmlParser parser, final Array<Actor> parsingResult) {
          final ObjectMap<String, Actor> actorsByIds = parser.getActorsMappedByIds();
          for (final String id : ids) {
              final Actor actor = actorsByIds.get(id);
              if (actor != null) {
                  attachListener(actor);
              } else if (!keep) {
                  parser.throwErrorIfStrict("Unknown ID: '" + id + "'. Cannot attach listener.");
              }
          }
          return keep;
      }
docs: Invoked after template parsing. Hooks up the listener to actors registered by "attachTo" attribute.
  
  @param parser parsed the template.
  @param parsingResult parsed actors.
  @return {@link LmlParserListener#REMOVE} by default. See {@link #setKeepListener(boolean)}.