xml in lua: how to say "ancestor"?

["Thomas A. Schmitz" <thomas.schmitz@uni-bonn.de>]

Hi all,

no real example, just snippets, sorry: I need to process xml documents 
in lua (because I want to collect information in tables). The structure 
is a bit irregular:

<document>
   <chapter title="One">
     <section title="One">
       <subsection title="One">
	Text
       </subsection>
     </section>
   </chapter>
   <chapter title="Two">
     <subsection title="One">
       Text
     </subsection>
   </chapter>
</document>

So chapters may or may not have sections. If, on the level of my 
subscetions, I want to extract the information of the chapter title, in 
a ConTeXt environment, I could say 
\xmlattribute{#1}{ancestor::chapter}{title}. How could I do the same in 
lua? I have something like
xml.attribute(e, "../../chapter", "title", "")
but that only works for the first case, not the second one. I tried to 
understand the lpegs in lxml-lpt.lua, but didn't succeed.

Thanks, and best wishes

Thomas
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