This is operator `~=`. I don't think it makes sense implementing it.
```D
MyFlags a = ...;
MyFlags b = ...;
a ~= b; //What? What the heck is that?
a &= ~b; //Ok, THAT makes sense.
```
If anything, arguably, that implementation would be operator `-=` (eg "remove"). But I think we don't want to introduce that. The idea is provide safety with the least surprise.