A callback method that is invoked immediately after the default change detector has checked the directive's data-bound properties for the first time, and before any of the view or content children have been checked. It is invoked only once when the directive is instantiated.
OptionalcheckboxItem: any
Siblings, except checkboxbuttons: Bootstrap 4 has no .btn-check, so its toggle buttons keep the nested input .btn-group-toggle documents.