Problem with understanding \doifemptyelse

["Gilles Pérez-Lambert" <Gilles.Perez@univ-montp3.fr>]

Hello,

I'm trying to setup headers in such a manner that on the left pages I 
have the chapter title and on the right the section one; but if there's 
no section, I want the chapter one...

I tried:
%%%%%%%%
\setupheadertexts
[][{%
\inframed[align=middle,frame=off,bottomframe=on,width=\makeupwidth]%
{\itx\hfill%
\doifemptyelse{\getmarking[section]}%%% If section header is empty
{\getmarking[chapter]}% Take the chapter one
{\getmarking[section]}}% else we take the section header
}]
[{\inframed[align=middle,frame=off,bottomframe=on,width=\makeupwidth]{\itx\
getmarking[chapter]\hfill\null}}][]
%%%%%%%%

I know I must miss something: \getmarking[section] is surely not that 
empty when there's nothing but my TeX knowledge is not that deep.

Another little problem: how not to have the headers on the beginning 
page of a chapter; i tried many things but didn't find the right one.

Thanks,

Gilles.