This is an identity document proving U.S. citizenship. Certificates of Citizenship are issued to derivative citizens and those who acquired U.S. citizenship (see definitions for Acquired citizenship and Derivative Citizenship).
The legislature occasionally skips outline levels.
For example:
(3) A person may apply [...]
(4)(a) A person petitioning for relief [...]
In this example, (3), (4),
and (4)(a) are all outline levels, but
(4) was
omitted by its authors. It's only implied. This presents an
interesting challenge when laying out the text. We've
decided to display a blank section with this note, in order
to aide readability.