The list widget displays an editable list of items in create or
edit mode, with additional message tag for errors, and the same list
of items in other modes. It is not usable within a list widget (see
sublist widget for this feature).
Items are defined using sub wigdets configuration.
This is actually a template widget type whose template uses a
<nxu:inputList /> tag in edit or create mode, and a table
iterating over items in other modes.
Since 5.6, it will apply to the current value (e.g. the layout or
parent widget value) if no field definition is given.