This is probably totally trivial, but what were the declarations that used to be there?? And why hasn’t it been removed???
Currently (probably Dec 2002 dev tools) it contains this:
#warning This header file is obsolete. #warning We do not know what you were trying to get from this header, but the declarations #warning are gone, and that was probably not the right way to go about things anyway. #warning This header will be removed completely December 1, 2002.
In 10.1 it contained a 1994-2001 copyright, and an import of General/NSCoder.h.
In 10.0 it contained a 1994-2000 copyright, an import of General/NSCoder.h, and an extra comment.
Obsolete header file
I don’t have any pre-10.0 machines around to test with. It probably dates back to General/NeXTStep or at least DP1. Whatever it is, it had something or other to do with General/NSCoder … maybe it’s so old that nobody at Apple can remember the reason it exists, or what harmful effects removing it might cause, so they wanted to give you a fair warning before ditching it. :-)