Dart Polymer Form Field Not Showing Validate Errors

I have code similar to this example working nicely with a sing-page app using AngularJS. I wanted to upgrade the page by using Dart and Dart-Polymer. In the HTML5 AngularJS versio

Solution 1:

I made a little test and experienced this: Validation only happens when submitting the form. Thus <form> tag is required around the input.

Validation happens then in both the regular case and the custom element. Maybe angular adds some special validation functionality?

Adding this works even without submitting the form in both cases:

<style>input:invalid {
    border: 1px solid #900;
  }
</style>

Regards Robert