Interesting, you gave me some hints which helped me putting the first pieces of the puzzle together. Thanks to you, I found the vB5_Template::render() method in vb/includes/vb5/template.php and made some successful tests. I immediately documented what I found and understood, you can read it here:
https://docs.google.com/document/d/1...it?usp=sharing
This will help me spread the knowledge to the other admins of our group. Again, I am not trying to find a fish to eat for one day, I am trying to learn fishing so I can feed myself for the rest of my life ;-)
If this can be useful to other VB people at the same time, all the better.
I look forward to your comments,
Thanks to everyone for your help!
Yann