-[NSApplication requestUserAttention:] return value?

FROM : Jim Correia
DATE : Wed Nov 07 17:39:09 2007

The documentation for -[NSApplication requestUserAttention:] says:

   The value returned by this method can be used to manually cancel a 
request by passing it as the parameter to cancelUserAttentionRequest:.

But it doesn't document the range of values returned. Empirically, it 
appears to be [0..N].

Can anyone confirm that to be the case? It would be nice to have an 
uninitialized/no-request value that I can stuff in my iVar rather 
than tracking whether I have an outstanding notification request 
separately.

Jim