The list widget allows you to create a repeatable item in the UI which saves as a list of widget values. map a user-provided string with a comma delimiter into a list. You can choose any widget as a child of a list widget—even other lists.
* **UI:** without any `fields` specified, the list widget defaults to a text input for entering comma-separated values; with `fields` specified, the list widget contains a repeatable child widget, with controls for adding, deleting, and re-ordering the repeated widgets.
* **Data type:** list of widget values
* **Options:**
*`default`: you may specify a list of strings to populate the basic text field, but declare defaults on the child widgets if you are specifying `fields`;
*`allow_add`: `false` hides the button to add additional items
*`collapsed`: when `true`, the entries collapse by default
*`summary`: specify the label displayed on collapsed entries
*`minimize_collapsed`: when `true`, collapsing the list widget will hide all of it's entries instead of showing summaries
*`label_singular`: the text to show on the add button
*`field`: a single widget field to be repeated
*`fields`: a nested list of multiple widget fields to be included in each repeatable iteration