- since the epoch, i.e. CLOCK_REALTIME. Either one of
- the two timestamp arguments may be passed as NULL in
- case the timestamp is not needed, but not both.</para>
+ since the epoch,
+ i.e. <constant>CLOCK_REALTIME</constant>. Either one
+ of the two timestamp arguments may be passed as
+ <constant>NULL</constant> in case the timestamp is not
+ needed, but not both.</para>