It's still using a subset of the comment syntax, and will still be ignored as comments rather than hard-fail in earlier versions.
Unknown attributes are also ignored silently, which isn't really a good sign.
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.