which (if any) events it's interested in for the next loop iteration.
* Edge-triggering available via EPOLLET or EV_CLEAR. These reduce wakeups
- for unidirectional classes (e.g. PublicInbox::Listener sockets,
- and pipes via PublicInbox::HTTPD::Async).
+ for unidirectional classes when throughput is more important than fairness.
* IO::Socket::SSL support (for NNTPS, STARTTLS+NNTP, HTTPS)