I haven’t found the source code of the append command anywhere and I’d like to know whether this command is guaranteed to be synchronous or not. So far I haven’t been able to come up with any test to figure it out.
For instance, something like this test won’t tell me exactly whether such command is synchronous or not… i mean, it seems the probability to be so is quite high and the common sense also tells this command should be a synchronous command but who knows… I don’t trust the common sense 
Could anyone please confirm me its nature or even better, where is it the source code of it hidden? So I won’t have any unexpected behaviour when using it on my commands