You're really doing a disservice to others with opinions that are so out of date.
Apparently there's now something called annotation routes. Which appear to be inferring functionality from comments.
You made me look though. I suppose I had it coming.
[0] https://www.php.net/manual/en/language.attributes.overview.p...
Unknown attributes are also ignored silently, which isn't really a good sign.
It may technically be forwards compatible syntactically (`#[foo]` will, as you say, just be ignored by PHP 7), but that's an anti-feature (assuming that the attribute isn't a no-op, it'll presumably break something else).
> `#[foo` used to be legal PHP 7, but is illegal in PHP 8).
So it is not a comment in PHP8 then.