Subheadings desired in XHTML 2.0

How does XHTML 2.0 deal with subheadings?  How should XHTML deal with
subheadings?

Do subheadings need a distinct element type?  Should subheadings be
children of headings rather than siblings of headings?

Given an article with the main heading "Foo" and with the subheading "Bar",
given the possibility of an element type 'sh' for subheadings, and assuming
that the examples are valid, which of the following document fragments is
most appropriate?  Why is that?

<!-- begin 1 -->
<h>Foo
   <sh>Bar</sh></h>

<!-- begin 2 -->
<h>Foo
   <h>Bar</h></h>

<!-- begin 3 -->
<h>Foo</h>
<sh>Bar</sh>

<!-- begin 4 -->
<h>Foo</h>
<h>Bar</h>

--
Etan Wexler <mailto:ewexler@stickdog.com>