/** @brief Activities
*
* This class is the ancestor of every activities that an actor can undertake.
- * That is, of the actions that do take time in the simulated world.
+ * That is, activities are all the things that do take time to the actor in the simulated world.
+ *
+ * They are somewhat linked but not identical to simgrid::kernel::resource::Action,
+ * that are stuff occurring on a resource:
+ *
+ * - A sequential execution activity encompasses 2 actions: one for the exec itself,
+ * and a time-limited sleep used as timeout detector.
+ * - A point-to-point communication activity encompasses 3 actions: one for the comm itself
+ * (which spans on all links of the path), and one infinite sleep used as failure detector
+ * on both sender and receiver hosts.
+ * - Synchronization activities may possibly be connected to no action.
*/
class XBT_PUBLIC Activity {
friend Comm;
