title: angular form validation `min` not working
body: <p>I am reading <a href="https://angular.io/guide/forms" rel="nofollow noreferrer">https://angular.io/guide/forms</a>.</p>
  
  <p>My codes:</p>
  
  <pre><code>  &lt;!-- Min price --&gt;
    &lt;div class="form-group"&gt;
      &lt;label for="minprice"&gt;Min price&lt;/label&gt;
      &lt;input type="number"
             min="0"
             class="form-control" id="minprice"
             required
             [(ngModel)]="model.minprice" name="minprice"
             #minprice="ngModel"&gt;
      &lt;div [hidden]="minprice.valid"
           class="alert alert-danger"&gt;
        Min price is required
      &lt;/div&gt;
    &lt;/div&gt;
  
    &lt;!-- Max price --&gt;
    &lt;div class="form-group"&gt;
      &lt;label for="maxprice"&gt;Min price&lt;/label&gt;
      &lt;input type="number" class="form-control" id="maxprice"
             required
             min="0"
             [(ngModel)]="model.maxprice" name="maxprice"
             #maxprice="ngModel"&gt;
      &lt;div [hidden]="maxprice.valid"
           class="alert alert-danger"&gt;
        Max price is required
      &lt;/div&gt;
    &lt;/div&gt;
  </code></pre>
  
  <p>I have two questions:</p>
  
  <p>1, <code>min="0"</code> seems not working. when I input <code>-1</code>, no error message shown.</p>
  
  <p>2, How to validate that <code>minprice</code> less than <code>maxprice</code>?</p>
  
  <p>Any hints welcomed. Thanks</p>