[QtQuick] Cannot use the "Select" (inspector) debugger feature (button is disabled, without any hint of what's required to enable it)

Hi!

I would like to inspect a QtQuick2 / Qt5.5 app in QT Creator 3.5.1 (by "inspect" I mean like I would using Ctrl+Shift+I in Chrome/Firefox, or in any GTK3 app).

The Debugging Qt Quick Projects / Inspecting User Interfaces documentation says it's possible using the "Select" tool, and it looks simpler and more integrated to QT Creator than GammaRay, so I'm trying to use it.

I am able to debug my QML app (e.g. I can set breakpoints in QML JS and successfully break) and did locate the tool (in the debug toolbar next to the threads combobox), but the button is always disabled / non-clickable (and so is the "Zoom" button, at its right), without any hint of why it's disabled and what's missing for it to be enabled.

I see three problems here:

1. (Short-term, to "just be able to use the feature") What am I missing to be able to use the feature?
2. Could the GUI tell it to me? (via a label or a mouseover text?)
3. Maybe the documentation could mention the requirements for the feature to work?