The specifically is currently defined by the initial contribution, which is the AsciiDoc Language docs hosted at
https://docs.asciidoctor.org/asciidoc/latest/ It's not "whatever asciidoctor specifies / does", but rather what's written in those docs. (However, where there are gaps, we do currently look at the implementation to fill in those details as is necessary. Translating the details into words is still a work in progress).
The specification project will build on the information in the AsciiDoc Language docs, though it will be written in a normative style. We haven't yet started that effort since the focus of the AsciiDoc WG so far has been on securing / protecting the AsciiDoc trademark and brand, developing a visual identity for AsciiDoc, relaunching
asciidoc.org, setting up new communication channels for the community, and formulating a program plan for the AsciiDoc WG. It has been a ton of work, but work that's crucial to establishing a foundation on which we can build.
You're welcome to participate in this effort to help move it forward. For the time being, I encourage you to join the AsciiDoc WG mailing list (
https://asciidoc-wg.eclipse.org/). We'll have information soon about a new communication channel that will make collaboration easier, so stay tuned for that too.
Best Regards,
-Dan