List<ClassDoc> getSubClasses() {
        return subClasses
    }
    void addSubClass(ClassDoc subClass) {
        subClasses.add(subClass)
    }
    ClassDoc mergeContent() {
        classProperties.sort { it.name }
        classMethods.sort { it.metaData.overrideSignature }
        classBlocks.sort { it.name }
        classExtensions.sort { it.pluginId }
        return this
    }

            DslDocModel model = createDslDocModelClosure(loadPluginsMetaData())
            def root = doc.documentElement
            root.section.table.each { Element table ->
                mergeContent(table, model)
            }
            model.classes.each {
                generateDocForType(root.ownerDocument, model, linkRepository, it)
            }
        }

        _ * classDoc.classExtensions >> []
        _ * classDoc.subClasses >> []

        when:
        def result = parse('<root/>')
        withCategories {
            renderer.mergeContent(classDoc, result)
        }

        then:
        formatTree(result) == '''<root>
    <chapter id="classId">
        <title>Class</title>
        <segmentedlist>

        when:
        ClassDoc doc = withCategories {
            def doc = new ClassDoc('org.gradle.Class', content, document, classMetaData, extensionMetaData)
            builder.build(doc)
            doc.mergeContent()
        }

        then:
        doc.classExtensions.size() == 2

        doc.classExtensions[0].pluginId == 'a'
        doc.classExtensions[0].mixinClasses == [extensionA1, extensionA2] as Set