Adding new elements into a private namespace

safer, cleaner but not very nice

# namespace for new elements
namespace a = "urn:cz-kosek:ns:assembler"

# import DocBook schema
include "docbook.rnc"

# two new elements are directly combined into pattern
a.inlines = element a:register { text }
            | element a:instruction { text }

# add new inlines to general inlines
db.general.inlines |= a.inlines