There are still the design docs (http://design.perl6.org/) which are essentially spec documents. They are what implementors have been using over the years. Don't forget the tests came from Pugs and now Rakudo is using the same test suite, so it's more portable than you perhaps imagine. The tests are the stamp of approval for a version number conformance. If you can pass all the versioned tests then you are that version of the language. I think that's a lot stronger statement than the engineers think they understood a spec document, even if formally specified. What are your thoughts on why that isn't ok or worse than relying on pure docs?