ECS FrameSetDocument extend Document

Hi ,
 
I'm curious as to why org.apache.ecs.FrameSetDocument doesn't extend
org.apache.ecs.Document.
 
In the past I've written a number of methods which returned the Document
class. Today I need to return a document containing frames from one of those
methods, and found myself writing this code:
 
    Document d = new Document ();
    d.setHtml (new FrameSetDoc ().getHtml ());
    return d;

 
Note that FrameSetDoc extends FrameSetDocument and builds the frameset.
 
Can someone satisfy my curiousity as to why this is so?
 
Regards,
    Mathew

-- 
Mathew Pole 
Web Developer, Custom Press 
email: [email protected] 
phone: 08 8269 0511 ext 313, fax: 08 8340 1212, mobile: 0403 164 617