-- Destroys the given user interface (recursively), or all user interfaces if none is provided.
function destroyGUI(guiNode)
    if not guiNode then
        guiNode = guiRoot
    end

    local guiElements = getElementData(guiNode, "guiElements", false)
    if type(guiElements) == "table" then
        for _, guiElement in ipairs(guiElements) do
            if isElement(guiElement) then
                destroyElement(guiElement)
            end
        end
    end

    for _, subGuiNode in ipairs(getElementChildren(guiNode)) do
        outputDebugString(getElementID(subGuiNode))
        destroyGUI(subGuiNode)
    end

    destroyElement(guiNode)
end