"A common error is to assume that attached properties and signal handlers are directly accessible from the children of the object to which these attributes have been attached. This is not the case. The instance of the attaching type is only attached to specific objects, not to the object and all of its children."

The following code located inside component pushed to StackView:

    Component.onCompleted: {
        console.log(StackView.index + " is stack index of the item")
    }

Gives the following error:

qrc:/content/IdlePage.qml:18: ReferenceError: StackView is not defined

But the manual states:

Attached Property Documentation

[read-only] StackView.index : int

This attached property holds the stack index of the item it's attached to, or -1 if the item is not in a stack.

What I am missing?

You can't do parent.view.push, but you can do parent.push. But that's not very convenient if you're not in the root Item.

I've found that the id: of the StackView is visible in its children, so if its id: is stackView, you can do stackView.push() anywhere in the child.