I am not able to validate a field

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i am using UI component form with some additional attribute field using HTML template. but I am not able to validate these field as par standard. required property is not working.

            <label class="attr-label" for="nego">Nego </label> 
            <select  required   data-form-part="merchandising_builder_form" name="nego[]" class="negolist " id="nego" multiple size="8"     
                    data-bind="options: negoOptions, 
         optionsText: 'value', optionsValue: 'id'  ">

            </select>   
        </section>  ```