This new option is shown whenever a simple line symbol or marker line symbol is used as part of a fill symbol for rendering polygons. The default behavior is to render both interior and exterior rings, but this new setting allows users to set the symbol layer to render only for the exterior ring OR only for interior rings. This allows for symbolisation which wasn't directly possible before, such as a marker line with markers for interior rings angled toward the interior of the polygon.
This feature was funded by QGIS User Group Germany
This feature was developed by Nyall Dawson (North Road)