code: public void addValidator(final FieldValidator validator) {
  		WComponent labelField = findComponentForLabel(field);
  
  		if (labelField instanceof Input) {
  			((Input) labelField).addValidator(validator);
  		}
  	}
docs: Adds a validator to the input field.
  <p>
  The validator will only be added if the field is a {@link Input} component.
  </p>
  
  @param validator the validator to add.