I noticed this with https://doc.qt.io/qt-5/qjsengine.html#qjsEnginex
The code looks like this:
but it's documented as
QJSEngine *QJSEngine::qjsEngine(const QObject *object)
It should not have the QJSEngine:: prefix, because as the heading says, it's related but it's not a member function. When you want to use this function, it's without the scoping prefix.