Get the regions needed to create the overview form.
array Example usage:
return array(
'content' => array(
// label for the region.
'title' => t('Content'),
// Indicates if the region is visible in the UI.
'invisible' => TRUE,
// A mesage to indicate that there is nothing to be displayed in
// the region.
'message' => t('No field is displayed.'),
),
);
public abstract function getRegions();