Angular.js Form Invalid- Don't know why - angularjs

Question

I don't know why, but by default in Angular.js this for is invalid by dafault(no interaction on the form):
<!-- Persistence -->
<div class="col-sm-6" ng-class="{'has-error': form.persistence.$dirty && form.persistence.$invalid}">
<div class="checkbox">
<input for="persistence" type="checkbox" ng-change="resetPersistenceInputBox(form, vip)" ng-model="persistanceCheckbox" ng-init="persistanceCheckbox=false">Client IP Based Persistence
<div>
<label class="control-label" style="font-weight: bold">Enter CIDR Netmask</label>
<div class="input-group">
<span class="input-group-addon">
x.x.x.x/
</span>
<input type="text" class="col-sm-6 form-control" id="persistence" ng-init="persistanceCheckbox=false" name="persistence"
ng-disabled="!persistanceCheckbox"
ng-required="persistanceCheckbox"
ng-model="vip.algorithm.persistence"
ng-pattern='/^([0-9]|[12]\d|3[0-2])$/'
ng-trim="true"
placeholder="Enter a netmask between 0-32">
</div>
<div class="help-block" ng-show="form.persistence.$dirty && form.persistence.$invalid">
<span ng-show="form.persistence.$error.pattern && form.persistence.$dirty">Netmask must be a number between 0-32.</span>
<span ng-show="form.persistence.$error.required">CIDR Netmask is required while "Client IP Based Persistence" is checked.</span>
</div>
</div>
</div>
</div>

Answer 1

Your form is not valid until you type the input
<input type="text" class="col-sm-6 form-control" id="persistence" ng-init="persistanceCheckbox=false" name="persistence"
ng-disabled="!persistanceCheckbox"
ng-required="persistanceCheckbox"
ng-model="vip.algorithm.persistence"
ng-pattern='/^([0-9]|[12]\d|3[0-2])$/'
ng-trim="true"
placeholder="Enter a netmask between 0-32">
The input is required with ng-required="persistanceCheckbox"
and must meet the ng-pattern : ng-pattern='/^([0-9]|[12]\d|3[0-2])$/'