Message subscription token for nodes.

Example

-- You can store a message handler token in a global variable and use it to acknowledge that the message handler is already installed.
if selectionChangedToken == nil then
    local handler = function(arguments)
        local source = arguments:getSource()
        local name = source:getProperty(Node.NameProperty)
        arguments:setHandled(true)

        print("Message from " .. name)
    end

    local textBox = contextNode:lookupNode("TextBox")
    selectionChangedToken = textBox:addMessageHandler(TextBoxConceptMetadata.SelectionChangedMessage, handler)
end

Example

-- You can use the previously stored token to remove a message subscription.
if selectionChangedToken ~= nil then
    local textBox = contextNode:lookupNode("TextBox")
    textBox:removeMessageHandler(selectionChangedToken)
    selectionChangedToken = nil
end