The default namespace, not surprisingly, is awk.
All of the predefined awk and gawk variables
are in this namespace, and thus have qualified names like
awk::ARGC, awk::NF, and so on.
Furthermore, even when you have changed the namespace for your
current source file (see Changing The Namespace), gawk
forces unqualified identifiers whose names are all uppercase letters
to be in the awk namespace. This makes it possible for you to easily
reference gawk’s global variables from different namespaces.
It also keeps your code looking natural.