Adding an external backend as an output formatter

Although the popular Asciidoctor.js backends are supported in this plugin suite, there is a good chance that one might want to use a backend that is not directly supported. For this there is a special output formatter of type AsciidoctorjsGenericOutputFormatter.

import org.asciidoctor.gradle.model5.js.formatters.AsciidoctorjsGenericOutputFormatter

asciidoc {
  toolchains {
    asciidoctorjs.registeredOutputFormatters {
      myBackend(AsciidoctorjsGenericOutputFormatter) {
        backend = 'foo' (1)
        attributes( foo_color : 'black') (2)
        copyResources = false (3)
        enforcedDocType = 'book' (4)
        requires 'foo' (5)
        usePackage( 'asciidoctor', 'foo', '1.2.3') (6)
      }
    }
  }
}

1	Set the name of the backend
2	Set the specific attributes that this backend might require.
3	Set whether the backend should copy resources.
4	If the backend requires a specific kind of document type, set it here, otherwise leave it alone.
5	If one or more `requires` need to be passed to the engine, define them here.
6	Add the NPM package details. The first parameter is the scope and can be passed as `null`. The second parameter is the package name. The third parameter is something that can be lazy-evaluated to a version string.