Layers can be organized hierarchically. For example, certain layers can be grouped together. Choose "Group" in the context menu of the layer list (right-click the layer list). The selected layers will be replaced by a tree node that represents these layers. Click on the tree node to expand or collapse this group.
Once layers are grouped, they can be hidden or made visible with a single double-click on the node representative. The node representative also controls the appearance of the layers in the group: if a color or style is assigned to the representative, it overrides the respective style of all layers contained in the group. This way for example, the color of the layers contained in the group can be changed at once. To remove a color override of a node representative, set the color to "None".
To resolve a group, select the group representative and choose "Ungroup" from the context menu.
A variety of automatic grouping methods is provided. For example, the "Regroup views by layout index" from the layer context menu will collect all layers and put them into one group per layout shown in the panel.