code: public List<ValidationError> validateInput() {
          List<ValidationError> errors = new ArrayList<ValidationError>();
  
          for (FormSectionController section : getSections()) {
              for (FormElementController element : section.getElements()) {
                  if (element instanceof LabeledFieldController) {
                      LabeledFieldController field = (LabeledFieldController)element;
                      errors.addAll(field.validateInput());
                  }
              }
          }
  
          return errors;
      }
docs: Returns a list of validation errors of the form's input
  
  @return a list of validation errors of the form's input