How to implement custom binding expression?

[lee shinwell]

 Like OGNL expression, I need a new XML binding expression.
This XML expression can read property from XML document object and 
update property to XML document object, no JavaBean object needed.
For example: 
<input jwcid=" [EMAIL PROTECTED]" value="xml:doc.name <http://doc.name/>"/>
<input jwcid="[EMAIL PROTECTED] " value="xml:doc.age"/>

doc is a XML document object:
<person>
 <name>Tim Robbin</name>
<age>28</age>
</person>