Chart draws each chart layer-by-layer, then presses these layers on top of each other to draw the final chart. Chart core, the internal charting engine, creates the layers one-by-one, depending on the developer’s settings, and then presses them together to create the final chart.
This architecture allows the application developer to extend the chart easily and with maximum flexibility. The Chart layers framework allows an application developer to slide a custom layer in the existing "deck" of layers.
For tasks that are too complicated or customized to be achieved by setting properties in an Chart, a custom layer can be implemented (see the red "Custom Layer" in the screen shot below). In a custom layer, the developer can draw additional graphics on the chart area, or modify existing ones.