+We introduce the notion of \fBtracing domains\fP which is essentially a type of
+tracer (kernel or user space for now). In the future, we could see a third
+tracer being for instance an hypervisor. For some commands, you'll need to
+specify on which domain the command applies (-u or -k). For instance, enabling
+a kernel event, you must specify the kernel domain to the command so we know
+for which tracer this event is for.
+