General structure of customization

in compact syntax:

include "docbook.rnc"
{
  ... redefinitions ...
}

... new patterns and combined patterns ...

in XML syntax:

<grammar xmlns="http://relaxng.org/ns/structure/1.0">
  <include href="docbook.rng">
    ... redefinitions ...
  </include>
  ... new patterns and combined patterns ...
</grammar>