Failing to run QML RangeSlider customization example

I was trying to repeat the example QML code in https://doc.qt.io/qt-5/qtquickcontrols2-customize.html#customizing-rangeslider

I've simply opened up the PySide2 source examples/declarative/signals/pytoqml1/view.qml file, and replaced the control that is placed on the static rectangle (I also disabled the timer in the project so that it doesn't interfere).

I am getting "ReferenceError: first is not defined" style errors involving both "first" and "second".

To be fair, I would be surprised if it was related to the fact that I was using PySide2, but still a factor to consider.

I'll try (I'm a complete noob to QML) adding "control" in front of the first.... references within the handle x/y position updating code, see what happens, in that case it may likely turn out to be a documentation problem and I will try to follow up with that information soon.