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
Furthermore fields which are listed in transOrigPointerField, languageField, label and type are automatically added to this list of fields and do not have to be mentioned again here.
Example from "sys_filemounts" table:
'ctrl' => [ 'shadowColumnsForNewPlaceholders' => 'sys_language_uid,l18n_parent,colPos', ... ],