Representing LALR(1) grammars in a schema?

Hi.  I need to describe a little language in XML, and I want to write a
schema to validate the XML stream.  The language is described by
a grammar, and it is embedded in a bunch of other stuff.

My (quick) reading of the XML Primer leads me to believe that the
most complex class of things that can be described by a schema
are regular expressions, and that it simply isn't possible to translate
my grammar into a schema.

Is my thinking correct?

-- jeff