How to add marcos

I want to add a macro to run on after expantion. The help give the following syntax

AFTER_EXPAND(Argument As String)

MsgBox Argument

AFTER_EXPAND = True

End Function

Many of the MNU commands appear to be intended to run from a button.

The AFTER_EXPAND appears to be event driven. I want to execute some code after the expansion event. I assume I put my code into the function above. Where do I put the function to ensure it gets executed? I tried adding it to sheet 1 (data cache) and the VBA came p as invalid syntax

I added the word "function" to the start and the error went away but there is no evidence the macro is invoked when I expand my schedule.

I need guidance getting started.

Thanks

Cliff