ClassDoc extensionA2 = classDoc('org.gradle.ExtensionA2')
        ClassDoc extensionB = classDoc('org.gradle.ExtensionB')
        _ * docModel.getClassDoc('org.gradle.ExtensionA1') >> extensionA1
        _ * docModel.getClassDoc('org.gradle.ExtensionA2') >> extensionA2
        _ * docModel.getClassDoc('org.gradle.ExtensionB') >> extensionB

        def content = parse('''<section>
                <section><title>Properties</title>

        if (classDoc == null && getFileForClass(className).isFile()) {
            return getClassDoc(className)
        }
        return classDoc
    }

    gradlebuild.docs.dsl.docbook.model.ClassDoc getClassDoc(String className) {
        gradlebuild.docs.dsl.docbook.model.ClassDoc classDoc = classes[className]
        if (classDoc == null) {

                classExtensionDoc = new ClassExtensionDoc(pluginId, classDoc);
                plugins.put(pluginId, classExtensionDoc);
            }
            classExtensionDoc.getMixinClasses().add(model.getClassDoc(mixin.getMixinClass()));
        }
        for (ExtensionMetaData extension : classDoc.getExtensionMetaData().getExtensionClasses()) {
            String pluginId = extension.getPluginId();

            // Assume this is a class and so has implemented all properties and methods somewhere in the superclass hierarchy
            ClassDoc superClass = model.getClassDoc(superClassName);
            classDoc.setSuperClass(superClass);
            superClass.addSubClass(classDoc);
        }

        List<String> interfaceNames = classMetaData.getInterfaceNames();