کار نکردن ng-minlength و ng-msxlength در AngularJS

[forodo]

سلام
چرا این دوتا پیغام خطاشون نشون داده نمیشه؟

<input type="number" name="number" placeholder="Your number" required ng-model="number" ng-minlength="15" ng-maxlength="100" />
<span style="color: Red;" ng-show="MyForm.number.$dirty && MyForm.number.$invalid">
<span ng-show="MyForm.number.$error.required">number must enter</span>
<span ng-show="MyForm.number.$error.number">Invalid number</span>
<span ng-show="MyForm.number.$error.minlength">Minlength is 0</span>
<span ng-show="MyForm.number.$error.maxlength">Maxlength is 15</span>
</span>