I wrote a automated c++ com add-in to make my c++ functions available as
Excel worksheet functions. For further improvements I would like to know

1. Is there any way to retrieve a Excel::RangePtr to the cell calling the
current function? I used a VARIANT* for return value, but it is initialized
"VT_EMPTY" and does not yield any information about the caller.

2. How can I make an argument of my function optional (in Excel)?

3. Is it possible to add these little descriptions about function and
arguments to my own com add-in functions, like they are available for the
build in functions in the paste function dialog?