qmllint: Tumbler: attached properties of Tumbler must be accessed through a delegate item

import QtQuick.Controls 2.15
import QtQuick 2.15

Tumbler { 
  delegate: Text {
     readonly property real angelVal: Tumbler.displacement / (Tumbler.tumbler.visibleItemCount / 2)
  }
}

import QtQuick 2.15

Text {                                                                                                                                                                            
    id: delegate                                                                                                                                                                                                                                                                                                                                                    
    readonly property real angelVal: Tumbler.displacement / (Tumbler.tumbler.visibleItemCount / 2)
}