ipp_request_t union help

I am looking at exposing the IPP functions of CUPS in the Net::CUPS perl 
package that I have put together, but have run into an issue that I need 
some clarification.

How does one know what struct is active in the union of structs in 
ipp_request_t (any, op, status, event)?

Usually a field exists in the struct to indicate which is "active".  I 
look at the code a bit and didn't see anything obvious.  I am sure I just 
missed it.


//========================================================\\
||  D. Hageman                    
<dhageman-QTp0yWLdihxBDgjK7y7TUQ@xxxxxxxxxxxxxxxx>  ||
\\========================================================//