Using the same principles as gradient editing, transparency editing lets you customize a gradient but just on the alpha channel in your design. This allows for more complex transparency gradients to be made, and then applied to object fills and strokes.
You can introduce more than two alpha levels along the gradient path, adjust where each stop is positioned and/or control alpha transitions. You can do this in two ways.
Using the former, you modify the transparency gradient by eye; the latter lets you design with precision and absolute control.
The following settings can be adjusted in the dialog: