We do both actually.

It's both nested and annotated with a depth attribute.  We want to know 
each quote block's depth in order to setup the right class type for CSS 
which handles the color-coding and indentation by quote depth number 
(the deeper you go the different colors you see and the more indent 
there is).  We could absolutely calculate the depth number dynamically 
by walking up the tree during the message display, but why force a 
discovery when you can have your answer pre-calculated.  It's not like 
the email is ever going to change.  :)

-jh-

Elliotte Rusty Harold wrote:
> One thing I noticed in your keynote Wednesday was that the expanded XML 
> uses elements like
> 
> <quote depth="1">
> 
> I may not remember the syntax exactly, but I assume this is just 
> indicating quotes of quotes and so forth. Why use the depth attribute 
> here instead of just having multiple nested quote elements?
> 
> Just guessing, but perhaps this is an area where overlap raises its head 
> since e-mail messages aren't really XML?
>