What is --extension in win32.api?

[Francois Gouget]

In a number of places in win32.api I see '--extension' is used. For 
instance for 'advapi32.dll' we have:

%long --extension

LSA_HANDLE

'--extension' is also used for pointer types in other places.

However, when I check winapi.pm I see that '--extension' is not used 
anywhere ($extension is set but never used). So what is it for? Is it 
obsolete and thus ripe for removal?