Protected Overrides Function MeasureOverride(ByVal availableSize As Size) As Size
    Dim desiredSize As New Size()
    For Each child As UIElement In VisualChildren
        child.Measure(availableSize)
        ' do something with child.DesiredSize, either sum them directly or apply whatever logic your element has for reinterpreting the child sizes
        ' if greater than availableSize, must decide what to do and which size to return
    Next child
    ' desiredSize = ... computed sum of children's DesiredSize ...
    ' IMPORTANT: do not allow PositiveInfinity to be returned, that will raise an exception in the caller!
    ' PositiveInfinity might be an availableSize input - this means that the parent does not care about sizing
    Return desiredSize
End Function