gtk-doc no main xml generated

[Andrea Zagli <azagli libero it>]

i followed the tutorial to enable my library to build gtk-doc

https://developer.gnome.org/gtk-doc-manual/unstable/

but when i run the first make, gtk-doc doesn't generate the main xml  
file (DOC_MAIN_SGML_FILE) (as the tutorial says it should do  
https://developer.gnome.org/gtk-doc-manual/unstable/settingup_firstrun.html.en)

it correctly generates *.types and *.txt

what could i have forgotten to do?

you can find files

http://saetta.ns0.it/gitweb?p=zakform/libzakform;a=tree;h=6b624574f31f9997d9fd4db927a0c54def6670eb;hb=6b624574f31f9997d9fd4db927a0c54def6670eb

thanks in advance