When you put <form>
tag inside you ngApp, AngularJS automatically adds form controller (actually there is a directive, called form
that add nessesary behaviour). The value of the name attribute will be bound in your scope; so something like <form name="yourformname">...</form>
will satisfy:
A form is an instance of FormController. The form instance can optionally be published into the scope using the name attribute.
So to check form validity, you can check value of $scope.yourformname.$valid
property of scope.
More information you can get at Developer's Guide section about forms.