Updated the error message of Widget.init.
Updated the error message of Widget.init.
GH-989 Carousel, Menu, Tabs: deprecate the 'open by default' option. Use select()/show() method instead.
GH-989 Collapsible: Set 'false' as default of this._shown.
GH-989 Popover: normalize private variables names to use shownby instead open/show