DOCBOOK-APPS: Problems validating author-element

[Joachim Ziegler <ziegler@mpi-sb.mpg.de>]

What am I doing wrong here:

     <author>
       <firstname>Joachim</firstname>
       <surname>Ziegler</surname>
       <email>ziegler@mpi-sb.mpg.de</email>
     </author>


xmlint says:

xmllint -valid --noout LEDATutorium.xml
LEDATutorium.xml:47: validity error: Element author content doesn't 
follow the Dtd
Expecting ((personname | honorific | firstname | surname | lineage | 
othername | affiliation | authorblurb | contrib+) , (personblurb | email 
| address)*), got (firstname surname email )
     </author>
             ^

But the content model is:

author ::=
((personname|
   (honorific|firstname|surname|lineage|othername|affiliation|
    authorblurb|contrib)+),
  (personblurb|email|address)*)


So <email> shoulf be allowed where it is, or am I missing something?

Greetings,
Joachim