complete Tag attribute in runtime

<?xml version="1.0"?>
<root>
     <foo someAtt/>

</root>

I want the attribute "someAtt" will be resoved  from the class Foo and show in complete dialog ,after type class name "Foo" or  click "Control+Space"

here is Foo.java

class Foo{

  public void setSomeAtt(String value)
  {......}

  public void setSomeAtt2(String value)
  {......}

}

I have already created an interface FooTag extends CommonDomModelElement, which method  or interface should I implement ?

thx.