DOCBOOK-APPS: How to match character data nodes in DSSSL

How do I match character data nodes in DSSSL, so I can apply some string
processing to text?  Conceptually, I'd imagine something like

(element (foo bar #PCDATA)
  (literal (magic-string-mangle-function (data (current-node)))))

If this doesn't work at all (or even if), does anyone have advice how to
do something about character entities that HTML browsers generally don't
understand, like — or „.

-- 
Peter Eisentraut             http://yi.org/peter-e/