How would one catch a delete key, backspace key, control X or other
indication that a user wants to delete the contents of a cell?

I used the example code in MSDN's "How to: Host Controls in Windows Forms
DataGridView Cells" as the basis for a GridDate column, I've created a
column that hosts a calendar control. However, there are times when this
cell must have no date specified and I do that by displaying a blank cell.
So far so good. What I can't figure out is how to go from some value to no
value. What if my user wants to get rid of the entered cell value? I can't
quite seem to figure out how to catch a delete key, backspace or control X
event on this cell. Any suggestions would be appreciated.