similar to \fIpoll(2)\fP's pollfd structure to be waited on in the same call.
On completion, if \fInumfds\fP is supplied, it will be populated with the
-number of file descriptors on which interesting events occured.
+total number of file descriptors on which interesting events occured. This
+number can include both libcurl internal descriptors as well as descriptors
+provided in \fIextra_fds\fP.
If no extra file descriptors are provided and libcurl has no file descriptor
to offer to wait for, this function will return immediately.