It seems like a more in depth documentation of the language. But at the same time last significant updates have been done years ago. The text is full of TODOs and outdated information (it says setters should refer to the backing field by using dollar as a prefix). The target site for the repository (http://jetbrains.github.io/kotlin-spec/) was updated years ago, even though fixes have been committed to the repository already.
What are the plans for this repository? Is this a language documentation draft, which will not be updated any more, or is this intended to be a reference for the language specification? Does it make sense to provide error reports/corrections (pull requests seem to be ignored).