frozen_string_literal: false
tk/optionobj.rb : control options for a group of widgets
NOTE: If you want to use key-only option (no value), use Tk::None for the value of the key-only option. e.g. hash_kv({'aaa'=>1, 'bbb'=>Tk::None, 'ccc'=>3}) => ["-aaa", 1, "-bbb", "-ccc", 3]