As far as I know, this is providing a better answer to "How do we know this is valid PHP code?" Currently, the answer to that question is "Because it does/doesn

As far as I know, this is providing a better answer to "How do we know this is valid PHP code?" Currently, the answer to that question is "Because it does/doesn't compile using the standard PHP interpreter." When this spec is finalized, the answer will change to "Because it does/doesn't follow the rules laid out in the PHP specification." In practice, there is a PHP spec, it's just an "unwritten" spec that is defined in the code of the PHP interpreter. With an official "written" spec, it will open the door to alternative PHP interpreters (like HHVM), since they will be able to say that they also support "PHP" as defined in the spec. Hope this helps!