Sublayers are a further subdivision of layers (see Layer), but there are some differences
Sublayers are automatically created when importing DXF/DWG files. A sublayer can be the Current layer.
When a sublayer and its parent layer have different attribute values, the weakest value wins. For example, when the layer is dimmed and the sublayer is visible, any object on the sublayer will still be dimmed.
A sublayer ID passed as a Scope ID, describes all objects on the sublayer.