Ok I installed the "Plugin manager" and found "C:\Program Files\XWindows Dock\Public Plugins\API" folder so that's a start.
But why no source for the Public Plugins themselves? C# source for GMail Checker would be a nice example to look at.
I do see cpp sources in "C:\Program Files\XWindows Dock\Plugins\ExampleDocklet\Source" but if you've already got C# code, that would save me some precious brainpower