CORRECT
http://qt-project.org/doc/qt-5/qtqml-syntax-objectattributes.html#attached-properties-and-attached-signal-handlers
This section describes "attached signal handlers", where the format is

<AttachingType>.on<SignalName>

Example: The Component type has a signal called completed and a corresponding attached signal handler called onCompleted.

WRONG
http://qt-project.org/doc/qt-5/qml-qtqml-component.html
This page has a section called "Attached Signals", and talks about the "onCompleted signal".

This mistake is repeated throughout the Qt documentation!