表单操作内部不接受加速移动页面项目中的“http url或自定义URL”

When we go to Accelerated Mobile Pages Project but inside the form action is not accepting "http url or custom url" lilke below :

<form method="post"
      **action="http://example.com"**   action-xhr="http://httpbin.org/response-headers"    target="_blank">
         <input type="title" name="term" required>
        <input type="submit" value="Submit">
</form>

Acknowledge please.