+questions group by index prefix 1.2.3 1.1 ...etc --> '1'
+
+NOTE: questions can contain parameterized exercises (how ?
+--> describe variables (syntax ?)
+--> write javascript script (OK, users trusted ? ==> safe mode possible if public website)
+Imaginary example: (using math.js)
+ <params> (avant l'exo)
+ x: math.random()
+ y: math.random()
+ M: math.matrix([[7, x], [y, -3]]);
+ res: math.det(M)
+ </params>
+ <div>Calculer le déterminant de
+ $$\begin{matrix}7 & x\\y & -3\end{matrix}$$</div>
+ * ...