> The "shall not be used otherwise" certainly covers any use that would
change the meaning of the token - like undefining it. Or using it as a name
in your own definition. So, you can actually name it, as long as that name
means what the implementation defined it to mean. Any change to that meaning
is IFNDR.

Additional case: "-U__GXX_MERGED_TYPEINFO_NAMES
-D__GXX_MERGED_TYPEINFO_NAMES=1".

I'm not sure whether it is an instance of "use".