More on Errors

Ok, I have been fiddling about a bit to see if I can suss
how errors work. If I send a request to a duff server, I
see that request->error_stack is not NULL. I can then find
out where (in which function) each error in the stack
occurred, but how I can find out what the error was?

Looking at HTError.c (I shouldn't have to look into a .c
file now should I) I see that there is a void* parameter
field with the comment "Explanation, e.g. filename" next
to it. Aha! But if it's a void* how on earth can I know
what it is?

IN the documentation (Using), at the end of the Error section,
it says "In the next section we will see how to display
errors in the application..." Alas the next section is
incomplete. Can someone help me sort this error business out?