You need to declare the "a"-type element in your DTD:
 
<!-- simple link declaration -->
<!--                         -->
<!ELEMENT a  (#PCDATA)>
<!ATTLIST a
	xml:link CDATA #FIXED "simple"
	href     CDATA #REQUIRED
	inline   (true|false) true
	content-role  CDATA ""
	content-title CDATA ""
	title    CDATA ""
	role     CDATA ""
	actuate  (user|auto) user
	show     (new|replace|embed) replace
	behavior CDATA ""
>
You'll also need to define the formatting in your style sheet. In HyBrick,
since we're using DSSSL/Scheme as the style language, this looks like:
(element a
  (make link
	destination: (entity-address (attribute-string "href"))
	  (make score
    	type: 'after
    	color: red-color)))
Best regards,
Ralph E. Ferris
Fujitsu Software Corporation