code: private Expression incrementKeyForTemplate(TemplateNode template) {
      Holder<Integer> keyCounter = keyCounterStack.peek();
      return JsRuntime.XID.call(
          Expression.stringLiteral(template.getTemplateName() + "-" + keyCounter.value++));
    }
docs: Returns a unique key for the template. This has the side-effect of incrementing the current
  keyCounter at the top of the stack.