Extending webdav?

Hi,

I have had a look through the documentation and I am a little unsure  
where I would start if I wanted to extend the webdav implementation,  
that is used by Jigsaw. Specifically I am looking to see what it would  
take to add support fo RFC 4791, known as Caldav. Caldav is an  
extenstion of Webdav, specifically for the exchange of calendar  
related data.

Any pointers and/or examples would be very much appreciated.

Andre