Attached property enum value cannot be used

import QtQuick 2.0

Rectangle {
    id: rect
    Accessible.role: Accessible.CheckBox

    Component.onCompleted: {

        console.log(rect.Accessible.role) // works, 44

        console.log(Accessible.Button)    // undefined

        Accessible.role = 1 ? Accessible.RadioButton : Accessible.CheckBox // Error: Cannot assign [undefined] to int

        console.log(rect.Accessible.role)

    }
}