+ <para>To destroy an event source object use
+ <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ but note that the event source is only removed from the event loop
+ when all references to the event source are dropped. To make sure
+ an event source does not fire anymore, even if it is still referenced,
+ disable the event source using
+ <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ with <constant>SD_EVENT_OFF</constant>.</para>
+
+ <para>If the second parameter of
+ <function>sd_event_add_time()</function> is
+ <constant>NULL</constant> no reference to the event source object
+ is returned. In this case the event source is considered
+ "floating", and will be destroyed implicitly when the event loop
+ itself is destroyed.</para>
+
+ <para>If the <parameter>handler</parameter> to
+ <function>sd_event_add_time()</function> is
+ <constant>NULL</constant>, and the event source fires, this will
+ be considered a request to exit the event loop. In this case, the
+ <parameter>userdata</parameter> parameter, cast to an integer, is
+ used for the exit code passed to
+ <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
+
+ <para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and
+ <constant>CLOCK_REALTIME_ALARM</constant> to define event sources
+ that may wake up the system from suspend.</para>
+
+ <para>In order to set up relative timers (that is, relative to the
+ current time), retrieve the current time via
+ <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ add the desired timespan to it, and use the result as
+ the <parameter>usec</parameter> parameter to
+ <function>sd_event_add_time()</function>.</para>
+
+ <para>In order to set up repetitive timers (that is, timers that
+ are triggered in regular intervals), set up the timer normally,
+ for the first invocation. Each time the event handler is invoked,
+ update the timer's trigger time with
+ <citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer
+ iteration, and reenable the timer using
+ <function>sd_event_source_set_enabled()</function>. To calculate
+ the next point in time to pass to
+ <function>sd_event_source_set_time()</function>, either use as
+ base the <parameter>usec</parameter> parameter passed to the timer
+ callback, or the timestamp returned by
+ <function>sd_event_now()</function>. In the former case timer
+ events will be regular, while in the latter case the scheduling
+ latency will keep accumulating on the timer.</para>
+