Interface definition for field widget plugins. This interface details the methods that most plugin implementations will want to override. See
public WidgetInterface::errorElement(array $element, ConstraintViolationInterface
public static WidgetInterface::isApplicable(FieldDefinitionInterface
public WidgetInterface::settingsForm(array $form, FormStateInterface
public WidgetInterface::massageFormValues(array $values, array $form
public WidgetInterface::formElement(FieldItemListInterface $items,
public WidgetInterface::settingsSummary()