In the setting tab for Layer, there are a few function like below.

Their role is to open the layer to be jumped and close other layers.

For example, there are the following steps.

1. Layer 0 is the default layer and is on. If you use T3 to open layer 3, set a T→2 on layer 3.
2. After pressing this T→2, layer 2 is opened and layer 3 is closed. The higheset opened layer is 2.

If T2 is used on T3 instead of T→2, layer 2 is turned on, but layer 3 is still on, so the highest opened layer is 3.

So the name is called To Layer. It actually performances is that you can jump from one layer to another layer, regardless of the status of all the layers.