Added two new options "Mask with Layer Above" and "Mask with Layer Below" in the "Extras" menu in the layers panel. Used to easily add masking layers from above or below to the active layer. (f702eba53f)
The bpy.typesGreasePencilLayer and GreasePencilLayerGroup are now subclasses of a new bpy.types.GreasePencilTreeNode. Common properties between layers and groups are now part of this base class. This also means that layer groups now have the channel_color and select property. (3ef2ee7c53)
The new GreasePencilTreeNode type now has two new properties (next_node and prev_node) to get the next/previous nodes at the same level in the tree. The next node is the node "above" in the tree and the previous node is the one "below". If the node is at the very top of its group, the next node is None. When it's at the very bottom, the previous node is None. (4229d7fa65)