Unknown error?

Hi,

I could not find this explained anywhere either in the text
of http://www.w3.org/TR/REC-xml nor could I find it reported
in http://www.w3.org/XML/xml-19980210-errata; namely:

   The LHS of production [30], namely extSubset, is used
   nowhere else in the grammar (i.e., in no other production),
   making it a useless grammar symbol.

Am I missing something? Please advise or explain.

Regards,

-hak