public Object exec(List args) throws TemplateModelException 
{
                int numArgs = args.size();
                if (numArgs != 1 && numArgs !=2) {
                    throw new TemplateModelException(
                            "?chunk(...) expects 1 or 2 arguments.");
                }
                Object chunkSize = args.get(0);
                if (!(chunkSize instanceof TemplateNumberModel)) {
                    throw new TemplateModelException(
                            "?chunk(...) expects a number as "
                            + "its 1st argument.");
                }
                return new ChunkedSequence(
                        tsm,
                        ((TemplateNumberModel) chunkSize).getAsNumber().intValue(),
                        numArgs  > 1 ? (TemplateModel) args.get(1) : null);
}