This interface allows WL8 to communicate with a chart in a ChildWindow instance. The WealthLab.WPF Chart class implements IChart. If you are implementing a ChildWindow in a Wealth-Lab extension, and it contains a chart, you can override the Chart property to return an instance of this interface.
WL8 calls this when the chart is visible and the user presses a keystroke. The Chart class in WealthLab.ChartWPF implements this call by putting the character pressed into the symbol entry field, and handling other special keystrokes such as backspace, and control left/right arrow.