Returns the region to which a row in the display overview belongs.
array $row: The row element.
string|null The region name this row belongs to.
public function getRowRegion($row) {
switch ($row['#row_type']) {
case 'field':
case 'extra_field':
return $row['format']['type']['#value'] == 'hidden' ? 'hidden' : 'content';
}
}