How is child property of type Item binded to parent?

bad63r

I am developing KDE app, where I have encountered this strange binding.

There is Object PlasmaComponents.Label, that contains property of type Item called toolTip, and that toolTip property is somehow connected to parent Object PlasmaCore.ToolTipArea.

PlasmaCore.ToolTipArea {
        id: toolTip

        property string text: model.display

        anchors.fill: parent
        active: root.visible && label.truncated
        mainItem: toolTipDelegate

        onContainsMouseChanged: item.GridView.view.itemContainsMouseChanged(containsMouse)
    }

    PlasmaComponents.Label {
        id: toolTipDelegate

        width: contentWidth
        height: undefined

        property Item toolTip

        text: toolTip ? toolTip.text : ""
    }

If someone can explain to me or point me to corresponding docs this property in PlasmaComponents.Label I would be really greatful.

 property Item toolTip

Best,
bad63r