i happened to want to change the roundup page title 
from a <h2> to <h1> (which, by the way, is the natural 
structural choice for a page title in HTML. the layout / 
font size can be easily changed with CSS). trying to do 
so in the classic template, i found this:

page.html (master page macro):

<td class="page-header-top" metal:define-
slot="body_title"><h2>name</h2></td>

with the body_title slot getting replaced in all the 
templates using this macro with something similar to this:

<td class="page-header-top" metal:fill-slot="body_title">
 <h2 tal:content="python:context._classname.capitalize
()+' editing'"></h2>
</td>

this means that to change the <h2> to <h1>, i have to 
replace <h2> with <h1> *in all templates filling the 
slot*, ie. in 16 files (the <h2> in page.html gets removed 
by macro expansion)! beside, all those 16 files repeat 
the same markup (<td class="page-header-top" ...>) - 
so if i want to change this, i have to do 16 replaces 
again. not good (style, maintainable) ...

this patch puts the <td class="page-header-top" ...> 
and the <h2> (which should be changed to a <h1> - see 
above) into page.html and removes it from the filling 
templates. to fill a slot without the html element that 
defines the fill, i use tal:omit-tag="python:1" in a 
defining <span>.

the patch applies with patch -p0 in the 
templates/classic/html dir. a similar change should be 
applied to the 'minimal' templates (and possibly other 
slot fills with duplicate markup).