It is impossible to claim conformance to an ever evolving language specification without referring to a certain version/edition or whatever it will be called. There are open pull request and issues which cannot be sensibly addressed due to this issue, unless we're claiming this spec is still a draft, in which case it is not really helpful for alternative implementations at all.
In theory we have branches for specific versions, but in practice there is no bandwidth to maintain multiple versions of the specification. Langspec master targets current PHP master.
It is impossible to claim conformance to an ever evolving language specification without referring to a certain version/edition or whatever it will be called. There are open pull request and issues which cannot be sensibly addressed due to this issue, unless we're claiming this spec is still a draft, in which case it is not really helpful for alternative implementations at all.