What exactly is done in the default gather stats job run in autotask in 12.1.0.2?

For Oracle 12c:
Does the default gather statistics job as scheduled in autotask do the following:
a)Gather system stats?
b)Gather the fixed object stats DAILY? For this one I read in the doc that "Oracle Database automatically gathers fixed object statistics as part of automated statistics gathering if they have not been previously collected". If they have been collected once by this job, does it stop gathering them? It says they should be gathered often to be current so if it stops gathering then I need an additional job.
c)Is there anymore detailed information on what this job does exactly. The doc is pretty vague saying "