The `choice-item' Widget
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Syntax:
ITEM ::= (choice-item [KEYWORD ARGUMENT]... VALUE)
The VALUE, if present, is used to initialize the `:value' property.
The value should be a string, which will be inserted in the buffer as a
button. Activating the button of a `choice-item' is equivalent to
activating the parent widget. This widget will only match the
specified value.