/usr/lib/ruby/2.3.0/tkextlib/bwidget/ is in ruby2.3-tcltk 2.3.0-5ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/2.3.0/tkextlib/bwidget/arrowbutton.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/bitmap.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/button.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/buttonbox.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/combobox.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/dialog.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/dragsite.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/dropsite.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/dynamichelp.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/entry.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/label.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/labelentry.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/labelframe.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/listbox.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/mainframe.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/messagedlg.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/notebook.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/pagesmanager.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/panedwindow.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/panelframe.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/passwddlg.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/progressbar.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/progressdlg.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/scrollableframe.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/scrolledwindow.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/scrollview.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/selectcolor.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/selectfont.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/separator.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/setup.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/spinbox.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/statusbar.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/titleframe.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/tree.rb
/usr/lib/ruby/2.3.0/tkextlib/bwidget/widget.rb