ok, starting to make sense 
So the “AsciiDoctor” syntax (which they still call “AsciiDoc”) is a superset of the official “AsciiDoc” syntax (from Eclipse), adding some new elements (and they don’t say explicitly which ones they add, they just mention two here but since they say “such as”, it hints that there could be more…).
I think the 2 they mention correspond to:
- Font Icons Mode | Asciidoctor Docs
- Button and Menu UI Macros | Asciidoctor Docs (btw they say
button:but it seems it’s a bug and it’sbtn:in practice.
It’s a pity they don’t specify in AsciiDoc Language Documentation | Asciidoctor Docs when it’s the official syntax and when it’s addition to the syntax.
Actually I wonder if there isn’t a single syntax which is “AsciiDoc” and that syntax is extensible with macros and AsciiDoctor just adds some more macros. If this is the case then there’s no “AsciiDoctor” syntax. In XWiki we have the same thing, and specific macros are not part of the syntax (it’s only the macro syntax that is part of the syntax).