designer-using-a-ui-file.html single inheritance aproach missleading in how to access the members.

"We can connect signals and slots in user interface widgets in the usual way, taking care to prefix the ui object to each widget used."

is missleading and technical incorrect. According to that, you would do "uioutputWidget->someF()".
(Someone on the qt help channel just did that, and its a common question how to access those widgets.)

Suggestion: "We can connect signals and slots in user interface widgets in the usual way. Remember that widgets are members of the ui object. \sa designer-calculatorform.html"
or add an example inline.