An example design hierarchy showing an unreachable widget. There is a Session Shell containing a Form widget. The Form has two children--a PushButton and a RowColumn. The RowColumn contains a PushButton named "b1". Callouts show that the Form has set the PushButton "b1" as its default button, the RowColumn has a "Function" structure and the PushButton "b1" has "Local" set as its Storage class.