I changed the line:
...and it worked
Thanks for all the suggestions.
And thanks for your feedback. I just learned something : this file belongs to xdg-user-dirs.
Extract of "apt-cache show":
Installed Size: 99190
It provides several commands, among which "xdg-user-dirs-update". Well, it's incredible in fact, there are many commands provided by this package, just type "xdg" and without leaving a space, hit tab, you'll see them all. I wonder all what we can do with them ?
I will have the use of it now, in the Openbox Mini project. I'll try it at once.