xmlToSmalltalkBinding heteregeneous collection, item class based on element content

Hi,

I'm trying to create an xmlToSmalltalkBinding to marshal/unmarshal following 2 xml elements.

(In the context of parsing Google API Contact feeds)

*** XML Element 1 ****

xml1 := '<feed>

<entry>

<category name="user"/>

<firstName>Ivo</firstName>

<lastName>Roefs</lastName>

</entry>

</feed>'

desiredObject := (Feed new)

entries: (User new firstName: 'Ivo'; lastName: 'Roefs'; yourself);

yourself

*** XML Element 2 ****

xml2 := '<feed>

<entry>

<category name="group"/>

<groupName>Smalltalkers</groupName>

</entry>

</feed>'

desiredObject := (Feed new)

entries: (Group new groupName: 'Smalltalkers'; yourself);

yourself

I started of with following binding description, but got stuck...

I can't figure out how to describe "entry" in the "feed" binding so that it refers to both User an Group. 

<schemaBindings>

<xmlToSmalltalkBinding targetNamespace="targetNamespace="urn:webservices"  defaultClassNamespace="MyCorp">

<object name="feed" smalltalkClass="Feed">

<element name="entry" aspect="entries" xpath="entry[category[@name='user']]"  maxOccurs="unbounded" minOccurs="0" ref="entry"/>

</object>

<object name="user" smalltalkClass="User">

<attribute name="firstName" ref="xsd:string"/>

<attribute name="lastName" ref="xsd:string"/>

</object>

<object name="group" smalltalkClass="Group">

<attribute name="groupName" ref="xsd:string"/>

</object>

</xmlToSmalltalkBinding>

</schemaBindings>

regards,

Ivo Roefs