customizing docbook-ng

What am I doing wrong here with the db.quote customization that is 
making it invalid?

Bruce

namespace db = "http://www.docbook.org/docbook-ng"
default namespace = "http://www.docbook.org/docbook-ng"

include "mods.rnc"

include "docbook-ng.rnc" {
# remove all the main software/technology related definitions
         db.domain.inlines = notAllowed
         db.product.inlines = notAllowed
         db.technical.blocks = notAllowed
         db.verbatim.blocks = notAllowed
         db.synopsis.blocks = notAllowed
# add a new element to quote
         db.quote = element quote { db.quote.attlist, (db.all.inlines | 
hb.nonquote)* }
# add mods to bibliography element
         db.bibliography = element bibliography {
                 db.bibliography.attlist,
                 db.bibliography.info,
                 db.all.blocks*,
                 (db.bibliodiv+ | (ModsSchema | db.biblioentry | 
db.bibliomixed)+)
                 }
}
# nonquote pattern allows for semantic rendering of split quotes like:
# "The world," the guy said, "is flat."
         hb.nonquote = element nq { empty }