DOCBOOK-APPS: Problems validating author-element

[Joachim Ziegler]

What am I doing wrong here:

    <author>
      <firstname>Joachim</firstname>
      <surname>Ziegler</surname>
      <email>[EMAIL PROTECTED]</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