Overriding behaviour of `is` for small-sized-optimized strings

[Per Nordlöw]

At

https://github.com/nordlow/phobos-next/blob/master/src/sso_string.d

I would like to override the behaviour of

     `x is y`

for `x` and `y` being instances of `SSOString`.

to always mean

     `x[] is y[]`

How do I do this?

Is this the recommended behaviour in D for small-size-optimized 
strings?