title: WPF Editable ComboBox
body: <p>I have a ComboBox and ComboBox.IsEditable property is set to True to have a ComboBox act as both a TextBox and a drop-down list simultaneously.  But when the ComboBox is data-bound, entering custom text will not cause a new item to be added to the data-bound collection.</p>
  
  <p>For example, if I enter 'Joe' in a ComboBox that is bound to a list of people, which doesn't contain the value 'Joe', then the value 'Joe' is not going to be added to the drop-down list automatically.</p>
  
  <p>What is the best way to handle this?</p>