This operator works the same as `?·` and `!·` combined:

```
·expansion ?· {·expansion} ·expansion !· {/* fallback expansion */}

// the equivalent new idiomatic syntax would be

·expansion ?!· {/* fallback expansion */}

```

See 8e4fe60d2396854aeaae94c0e0e00161acbb8326 for history of `?·` and `!·`.