It is possible to create a diagram that contains different layers of elements. Each layer and its elements will display together (unless you specify otherwise), but is treated as being completely separated from the other layers as far as editing is concerned.
We have already added a new rectangle to our example diagram. Now select View -> Layers to bring up the Layers menu.
The Layers menu appears on the right hand side of the screen, overlapping the Format Panel.
At the moment, the diagram contains only the default Backgrounnd level, which is the level you work on when you have only a single layer. The tick box indicates that all background elements (in this case, just the rectangle) as being displayed.
Let us now add a second layer. This is done by clicking the Add layer button at the bottom.
We have added a second layer on the top of the Background layer, which is called Layer 1. If we add new elements to the diagram now, they will be added as part of Layer 1. Let's add an ellipse.
Dragging the ellipse over the rectangle causes it to appear in front. We would expect this in any case, since new shapes will appear in front of older ones. However, if we right click the ellipse and click To back, the ellipse will still appear in front of the rectangle. Layer 1 elements will always appear in front of Background elements.
It can be confusing to view multiple layers at once. The option is therefore given to remove any or all of the layers from the display. Let us untick the Background box.
The rectangle has gone, but the ellipse in Layer 1 is still visible.
We can move elements to the next layer up, by selecting them and clicking the Move selection button. Let us retick the Background box, then select the rectangle, and move it to Layer 1.
Now that both shapes are in Layer 1, we are able to move either one in front of the other, as per usual.
We might want to duplicate one layer to form the basis for a new one. Now that we have two shapes in Layer 1, let us copy them into another new layer, Layer 2. No selection is needed; simply click the Duplicate Layer button, and copies of the shapes will appear over their originals. Notice that Layer 2 has also appeared in the list of layers.
We shall drag the new shapes down so that they are below the originals.
At this point we have a rectangle overlapping an ellipse in Layer 1, and the same in Layer 2. We might decide that we want to delete some of the layers. It is possible to delete any layer, including the Background layer. Note however that if there is only one layer left, and you try to delete it, the diagram will default back to having a Background layer, which cannot be deleted.
We can delete a layer by clicking the Remove Layer button.
Here we have removed the Background and Layer 1. Only the shapes in Layer 2 remain. The Layer 1 shapes were deleted along with Layer 1.