knockout/knockout — pull request #647 by mbest (2014-01-18 02:42:44+00:00)
Title: Support select value not in options list, optionally

Add an option for the `value` binding that prevents it from changing the view model value if the current value isn't in the list of drop-down values. I believe that all browsers will let you have no selection for a drop-down list by setting `selectedIndex = -1`.