There is wiring and state spanning multiple levels of container, to support the "show all parameters" feature. The current behavior is,
- Initially show the "add parameter" dropdown area with a limited number of c. 5 parameters.
- Final item is a "show all parameters" button. When clicked, show *all* of the template parameters.
- Once show all has been activated, there is no way to collapse the list again.
- Once show all has been activated, remember the choice and keep expanded if the user a) completes the action by choosing a named parameter or adding an unknown one, or b) deletes the placeholder item.
- Do not change behavior.
- Push "show all" feature down into the placeholder page.
- Remember state by persisting the entire placeholder page. This isolates container classes from state implementation and action wiring.