Currently, the QML ScrollBar implements the QAccessibleValueInterface (via its base classes), but doesn't report the actual scroll position, so the value (always 0.0) is useless/misleading. Instead, the actual scroll position should be reported.

Sample steps to reproduce on Linux (using the AT-SPI2 Value interface):

1. build and run the given sample program (based on the one from QTBUG-139833):

   import QtQuick
   import QtQuick.Controls
   import QtQuick.Layouts
   
   ApplicationWindow {
       visible: true
       title: qsTr("ScrollView example")
   
       ScrollView {
           anchors.fill: parent
           contentHeight: columnLayout.implicitHeight
           contentWidth: columnLayout.implicitWidth
   
           ColumnLayout {
               id: columnLayout
   
               Repeater {
                   model: 100
   
                   Text {
                       Accessible.name: text
                       Accessible.role: Accessible.StaticText
                       Layout.fillWidth: true
                       text: "Element %1".arg(index)
                   }
               }
           }
       }
   }
    

1. run Accerciser and select the object for the vertical scroll bar in the application's accessibility tree
2. using Accerciser's IPython console, query the current and min/max value:

   In [2]: value = acc.queryValue()
   In [3]: value.get_currentValue()
   Out[3]: 0.0
   In [4]: value.get_maximumValue()
   Out[4]: 0.0
   In [5]: value.get_minimumValue()
   Out[5]: 0.0
   

Actual result
0.0 is reported for all values.

Expected result:
Since the scroll bar is not at its maximum position (there are elements out of the range that can be made available by scrolling further down), the maximum value should be greater than the current value, and scrolling should be possible by setting a larger value using the API.