The official one is here: https://github.com/php/php-langspec

It was pushed quite strongly around the time when HHVM was striving for high compatibility with PHP (they've since dropped that goal).

That's cool. I had to learn some intricacies of PHP for a job once quite a while ago and the docs weren't quite sufficient. Could have used that. Language specs are typically harder to digest then other material but ultimately you can get all the details out of them you need and they're typically worth reading.

No, just a hammer.

https://blog.codinghorror.com/the-php-singularity/