Markup: templates/output/04-elements/forms/input/week.html
<div class="form-group">
<label for="demoformid-idw">Choose a calendar week as appointment</label>
<input class="" type="week" id="demoformid-idw" name="" value="1970-W01"/>
</div>
<div class="form-group has-error">
<label for="demoformid-idw-error">Choose a calendar week as appointment</label>
<input class="" type="week" id="demoformid-idw-error" name="" value="1970-W01"/>
<div class="form-group__error" role="alert">This field is required</div>
</div>
Source:
assets/sass/04-elements/_elements.forms.scss, line 210