/usr/lib/ruby/2.3.0/tkextlib/iwidgets/ 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/iwidgets/buttonbox.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/calendar.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/canvasprintbox.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/canvasprintdialog.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/checkbox.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/combobox.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/dateentry.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/datefield.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/dialog.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/dialogshell.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/disjointlistbox.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/entryfield.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/extbutton.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/extfileselectionbox.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/extfileselectiondialog.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/feedback.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/fileselectionbox.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/fileselectiondialog.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/finddialog.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/hierarchy.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/hyperhelp.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/labeledframe.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/labeledwidget.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/mainwindow.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/menubar.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/messagebox.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/messagedialog.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/notebook.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/optionmenu.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/panedwindow.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/promptdialog.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/pushbutton.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/radiobox.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/scopedobject.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/scrolledcanvas.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/scrolledframe.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/scrolledhtml.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/scrolledlistbox.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/scrolledtext.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/scrolledwidget.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/selectionbox.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/selectiondialog.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/setup.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/shell.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/spindate.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/spinint.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/spinner.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/spintime.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/tabnotebook.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/tabset.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/timeentry.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/timefield.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/toolbar.rb
/usr/lib/ruby/2.3.0/tkextlib/iwidgets/watch.rb