ssages. Unlike dictionary, One-Of will only let the users specify a single child at a time. The UI will allow users to pick which child they want to specify, and allow users to specify that child. Note that the child can be completely empty. One-Of’s are a great way to encode optional parameters, or parameters that only exist under circumstances. It is valid to have an empty One-Of child - that just means that if selected, that option has no additional parameters. Please see <a class="reference internal" 