help needed with grammar

["Pieter van der Spek" <pieter@West.NL>]

Below is part of a grammar I'm working on:

Helpers
   class = 'class';

Tokens
   class = class;

Productions
   // document
   document = P.class+;

   // classes
   class = T.class [class]:identifier inheritance_clause? class_body? end
[end]:identifier;

This gives the following error:
[474,15] class is an invalid element name.

Where [474, 15] denotes the line starting with document = ...

I don't understand why I'm getting this message. Is there anyone who can
explain this to me ?
Thanks in advance.

-------------------

Pieter van der Spek
---- West Consulting B.V.        - www.west.nl
---- Tu Delft / Computer Science - www.tudelft.nl