-The callbackreturns an integer indicating whether we managed to deal with
-the message. I admit that this semantic is a bit troublesome, it should be 0
-if we managed to deal properly with the message to mimic "main()" semantic.
-That's historical, but I may change this in the future (no worry, I'll add
-backward compatibility solutions). Here is the actual code of our callback:
+The callback returns an integer being its error code, just like the "main()"
+function. Here is the actual code of our callback: