I can't tell from reading this if id-of
returns a string or a keyword. The first paragraph says string, the second says keyword. I am going to have to try it and see, but it would be nice to be spared that step in the future. :)
Returns the id of the given widget if the :id property was specified at
creation. The widget parameter is passed through (to-widget) first so
events and other objects can also be used. The id is always returned as
a string, even it if was originally given as a keyword.
Returns the id as a keyword, or nil.