Undo / Redo Count?

[Tosh]

I'm using the Visio Drawing Control (VCD) hosted in a C# application.  Best
Practices say to use my own menus and toolbars rather than Visio's.  I have
toolbar buttons for Undo and Redo, and they work just fine.

What I want to do is disable Undo when there is nothing to Undo, and disable
Redo when nothing has been undone.  Is there something like an
UndoStack.Count on a page, document, or application object somewhere?

TIA