title: Tkinter: Listbox separators, disabled items, keyboard navigation?
body: <p>I'm studying the Tkinter Listbox widget and have been unable to find solutions for the following functionality:</p>
  <ol>
  <li><p>How can I create non-selectable horizontal separator items, eg. separators equivalent to the Tkinter Menu widget's .add_separator()? (Using chars like dashes and underscores looks awful).</p>
  </li>
  <li><p>How can I disable a specific item? I tried using .itemconfig( index, state='disabled' ) without success.</p>
  </li>
  <li><p>How can I enable keyboard navigation, eg. when a user's keyboard input automatically scrolls one forward to the closest item that begins with the text the user typed? Must I <code>bind(&lt;KeyPress&gt;, ...)</code> and manage this behavior myself?</p>
  </li>
  <li><p>Would some of the above functionality be easier to implement using a Text widget or the <code>ttk.Treeview</code> widget?</p>
  </li>
  </ol>