`const C = zlib.Gzip` stopped at SC2020, and `instanceof zlib.Gzip`
(any zlib class) stopped at SC1090. A const binding of a zlib class is
now a compile-time alias with no runtime slot: `new C()`, `typeof C`,
`C.name` and `C === zlib.Gzip` lower at the use. `instanceof` against a
zlib class asks the runtime for the stream's mode when the operand is a
Transform, tests for a Transform first when it is typed as one of
Transform's bases, and answers false for other static types, as in Node.
Other uses of an alias as a value report SC1090 at the use.
Chris Tate
b4ef932b72