Btw, I could circumvent the lack of a `setStyle` method, using the `setString` method of the parent object. That's not something we want to encourage, but you can use it as a workarround.
I confirmed that the setStyle method is not present in 1.6.0 either, apologies for the confusion. @gregopet, feel free to open an issue to add the method in the issues sectionhttps://github.com/asciidoctor/asciidoctorj/issues.
StructuralNode.setStyle() should be available in 1.6.0 but it's not available yet in a released version.
Therefore it's probably time for a new AsciidoctorJ 1.6.0-alpha.4 release with an updated Asciidoctor core.