At the startup, that undockable toolwindow was docked somewhere by default. That's not perfect for my purpose.
Actually, what I need is a top-most form, but just being top-most of the hosting applicatiion. So I couldn't simply set the TopMost property of the form to true, that's applied to all apps.
Besides, I just found that even after disabled all CanDock* and disabled the CanAttach property, it's still dockble to default dock location, the left area.
Is there a way to completely disable the docking feature of the tool window?