[Twisted-web] nevow HTML based template fragment problem

[Tazzo]

How can I insert a html rendered template inside another
html rendered template?
I mean, I have a rend.Page class with a docFactory that load
a template (ex: page.html) with a header tag to renderize.
The problem is that the header tag must be loaded from another
rend.Page class who have is docFactory template (ex: header.html)
to renderize, before send it. 
How can I use the header rend.Page class from a render method in
another rend.Page class?
 
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