Incomplete documentation qml (eg objectName), and Qml inheritance

http://doc.qt.nokia.com/4.7/qtbinding.html

it says

Rectangle {
anchors.fill: parent
objectName: "rect"
}

indicating Rectangle has a "objectName" property.

However

http://doc.qt.nokia.com/4.7/qml-rectangle-members.html

which is allegedly "he complete list of members for QML Rectangle Element, including inherited members." doesnt list this property

Presumably rectangle "inherits" from QtObject via Item (whatever "inherits" means exactly in Qml. But this inheritance is not documented either. What does "inheritance" mean exactly in this context? How does a Qml object inherit from another?