condition. When using a buffering BIO, like a BIO pair, data must be written
into or retrieved out of the BIO before being able to continue.
+SSL_shutdown() can be modified to only set the connection to "shutdown"
+state but not actually send the "close notify" alert messages,
+see L<SSL_CTX_set_quiet_shutdown(3)|SSL_CTX_set_quiet_shutdown(3)>.
+When "quiet shutdown" is enabled, SSL_shutdown() will always succeed
+and return 1.
+
=head1 RETURN VALUES
The following return values can occur:
L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_connect(3)|SSL_connect(3)>,
L<SSL_accept(3)|SSL_accept(3)>, L<SSL_set_shutdown(3)|SSL_set_shutdown(3)>,
+L<SSL_CTX_set_quiet_shutdown(3)|SSL_CTX_set_quiet_shutdown(3)>,
L<SSL_clear(3)|SSL_clear(3)>, L<SSL_free(3)|SSL_free(3)>,
L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>