angularjs - can't seem to display the content of ng-message for 'required' -

i don't know why can't seem display content of ng-message 'required'. i'm new this, please excuse if i'm missing obvious!!

if try display {{studentform.fname.$error}} says blank.

btw first question on stackoverflow :)

edit: use form tag instead of md-form. seems md-form not valid tag. additionally md-auto-hide="false" might me required under ng-messages tag. see : https://github.com/angular/material/issues/6767

<div layout="row">    <div layout="column">      <md-form ng-model="student" name="studentform" flex="90%">        <div layout="column" layout-padding>          <md-input-container class="md-block" flex>            <label for="firstname">firstname</label>            <input type="text" ng-model="student.firstname" name="fname" placeholder="firstname" required></input>          </md-input-container>          <div ng-messages="studentform.fname.$error" role="alert">            <div ng-message="required">required!!</div>          </div>          <md-datepicker name="dob" ng-model="student.dob" md-placeholder="enter dob" required valid>enter dob</md-datepicker>          <div ng-messages="studentform.dob.$error" role="alert">            <div ng-message="valid">the entered value not date!</div>            <div ng-message="required">this date required!</div>          </div>        </div>        <md-button ng-click="submit()">send message</md-button>      </md-form>    </div>  </div>

use form tag instead of md-form. seems md-form not valid tag. additionally md-auto-hide="false" might me required under ng-messages tag. see : https://github.com/angular/material/issues/6767