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There exist a million and one different ways to dynamically retrieve content. Your individual use case will be different to this dummy one, so you'll need to adapt the code shown here to your own situation. You should try to understand the concepts behind this code and how all of the pieces fit together so you can successfully change this example to work for you.
Your implementation may dynamically acquire content in any number of ways, i.e. via AJAX from databases, or following user input, and so forth... For this example we'll just use the following add and remove buttons: