customization layers in rnc?

Can someone please help me understand how to implement the following  
customization layer for the DocBook DTD in RNC?

Simply running Trang on it gets me the following error:

	dbcitx.dtd:21:67: fatal: syntax error

Bruce
------------------------------------------------------------------------ 
---------------------------------
<!-- This is a customization layer for DocBook XML 4.1.2 which  
implements
      RFE 810932 - improved citation support -->

<!ENTITY % citation.module "IGNORE">
<!ENTITY % citation.element "IGNORE">
<!ENTITY % citation.attlist "IGNORE">

<!ENTITY % blockquote.module "IGNORE">
<!ENTITY % blockquote.element "IGNORE">
<!ENTITY % blockquote.attlist "IGNORE">

<!ENTITY % quote.module "IGNORE">
<!ENTITY % quote.element "IGNORE">
<!ENTITY % quote.attlist "IGNORE">

<!ENTITY % epigraph.module "IGNORE">
<!ENTITY % epigraph.element "IGNORE">
<!ENTITY % epigraph.attlist "IGNORE">

<!-- load original DocBook stuff -->
<!ENTITY % DocBookDTD PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN">
%DocBookDTD;

<!-- extend the citation element.
      we add two attributes: renderas (select the processing  
expectations)
                             caption (provide additional text)
      we add one element:    Biblioref (extended bibliographic data)
-->

<!ENTITY % local.citation.attrib "">
<!ENTITY % citation.role.attrib "%role.attrib;">

<!ELEMENT biblioref - - EMPTY>
<!ATTLIST biblioref linkend IDREF #IMPLIED
                         endterm IDREF #IMPLIED
                         unit NMTOKEN #IMPLIED
                         start NMTOKEN #IMPLIED
                         stop NMTOKEN #IMPLIED
>

<!ELEMENT citation - - ((%para.char.mix;|biblioref)+)>

<!ATTLIST citation
                 %common.attrib;
                 %citation.role.attrib;
                 %local.citation.attrib;
                 renderas (full|author|year|title) "full"
                 caption CDATA #IMPLIED
>

<!-- done with the citation element -->

<!-- extend the blockquote element -->
<!ENTITY % local.blockquote.attrib "">
<!ENTITY % blockquote.role.attrib "%role.attrib;">

<!ELEMENT blockquote - - (title?, attribution?, (%component.mix;)+,  
biblioref?)>

<!ATTLIST blockquote
                 %common.attrib;
                 %blockquote.role.attrib;
                 %local.blockquote.attrib;
>

<!-- done with blockquote -->

<!-- extend the quote element -->
<!ENTITY % local.quote.attrib "">
<!ENTITY % quote.role.attrib "%role.attrib;">

<!ELEMENT quote - - ((%para.char.mix;)+, biblioref?)>

<!ATTLIST quote
                 %common.attrib;
                 %quote.role.attrib;
                 %local.quote.attrib;
>

<!-- done with quote -->

<!-- extend the epigraph element -->
<!ENTITY % local.epigraph.attrib "">
<!ENTITY % epigraph.role.attrib "%role.attrib;">

<!ELEMENT epigraph - - (attribution?, (%para.class;)+, biblioref?)>

<!ATTLIST epigraph
                 %common.attrib;
                 %epigraph.role.attrib;
                 %local.epigraph.attrib;
>
<!-- done with epigraph -->