string (list of field names)
When a new element is created in a draft workspace, a placeholder element is created in the Live workspace. Some values must be stored in this placeholder and not just in the overlay record. A typical example would be
sys_language_uid. This property defines the list of fields whose values are "shadowed" to the Live record.
All fields listed for this option must be defined in
Example from "sys_filemounts" table:
'ctrl' => [ 'shadowColumnsForNewPlaceholders' => 'sys_language_uid,l18n_parent,colPos', ... ],