code: public void add (VisValidatableTextField field) {
  		if (fields.contains(field, true) == false) fields.add(field);
  		field.addListener(changeListener); //addListener won't allow to add same listener twice
  		validate();
  	}
docs: Adds field to this form without attaching any {@link FormInputValidator} to it. This can be used when field
  already has added all required validators.