I'm glad you brought this up because we do need to eventually have a syntax definition for AsciiDoc that we can use as the basis of other parser tools. The obvious choice for this definition is a PEG grammar. I think we'll get there. Until then, the most readable definition thus far is probably the highlighter for GTK source view, which I've updated [1].
You can probably draw from the asciidoc.lang file from GTK source view and the Markdown definition for Kate [2] to create a new AsciiDoc definition for Kate. Start with the section titles and it goes pretty quickly.
-Dan