Why isn't there a `!in` or `!∈` function/operator?

[nilshg]

This is an old debate, see e.g.

Non-unicode versions of unicode functions in base/stdlib?

I’m looking at someone else’s code in Julia 1.0 and noticed they use the ∉ (not in) function, which doesn’t seem to have an ascii equivalent (e.g. notin). I realize that it’s possible to get the same functionality by typing ! (el in set), but it reminds me of the deprecation of @test_approx_eq in Julia 0.5 in favor of @test a ≈ b atol=ε in Julia 0.6. I have to say that I’m a little alarmed at the existence of unicode-only functions in base. I’ve seen people raise similar concerns in various pla…