QML anchor lines are not documented

QML Item's have anchor lines that can be bound to. E.g.;

Item {
   anchors.top: parent.top
}

It's not clear from the documentation that either Item has these anchor lines as properties, or that they are attached properties. It should be mentioned in the documentation, as the intuitive assumption from the pragmatic/pedantic user would be to use the less-elegant;

Item {
   anchors.top: parent.anchors.top
}