Validation on md-chips with md-autocomplete - angularjs

Question

I am trying to build a page that uses angular material and uses elements such as md-chips and md-autocomplete.
I want to put a validation on this md-chips so that an error message will appear if there are no chips and a submit button is clicked, similar to the md-input-container.
For the md-input-container my code is as follows
<md-input-container class="md-block" flex-gt-sm>
<label>Title</label>
<input md-maxlength="100" maxlength="100" required type="text" name="bookTitle" ng-model="bookCtrl.book.name">
<div ng-messages="bookForm.bookTitle.$error" role="alert">
<div ng-message-exp="['required', 'maxlength']">
Book title is required and it should not exceed 100 characters.
</div>
</div>
</md-input-container>
And an alert will appear if the validations are not met. How can I do something similar to the md-chips with md-autocomplete that has the following code
<md-chips name="bookAuthors" ng-model="bookCtrl.book.authors" md-autocomplete-snap
md-separator-keys="bookCtrl.keys"
md-transform-chip="bookCtrl.transformChip($chip)"
md-require-match="bookCtrl.authorAutocompleteRequireMatch">
<md-autocomplete
md-selected-item="bookCtrl.selectedAuthor"
md-search-text="bookCtrl.searchAuthor"
md-items="author in bookCtrl.querySearch(bookCtrl.searchAuthor, bookCtrl.bookAuthors)"
md-item-text="author.name"
placeholder="Author">
<span md-highlight-text="bookCtrl.searchAuthor">{{author.name}}</span>
</md-autocomplete>
<md-chip-template>
<span>{{$chip.name}}</span>
</md-chip-template>
</md-chips>
What can be added to the md-chips in order to perform validation?

Answer 1

Create div block outside of md-chips block and add red color. It will work similarly
<div ng-messages="{test:true}" ng-show="true">
<div ng-message="test" style="color: rgb(221,44,0); font-size:12px">errroro123</div>
</div>