ClassExtensionMetaData extensionMetaData = new ClassExtensionMetaData('org.gradle.Class')
        extensionMetaData.addMixin('a', 'org.gradle.ExtensionA1')
        extensionMetaData.addMixin('a', 'org.gradle.ExtensionA2')
        extensionMetaData.addMixin('b', 'org.gradle.ExtensionB')
        ClassDoc extensionA1 = classDoc('org.gradle.ExtensionA1')
        ClassDoc extensionA2 = classDoc('org.gradle.ExtensionA2')

    final Set<MixinMetaData> mixinClasses = []
    final Set<ExtensionMetaData> extensionClasses = []

    ClassExtensionMetaData(String targetClass) {
        this.targetClass = targetClass
    }

    def void addMixin(String plugin, String mixinClass) {
        mixinClasses.add(new MixinMetaData(plugin, mixinClass))
    }

    def void addExtension(String plugin, String extension, String extensionClass) {

                    extensions[targetClass] = extension
                }
                def mixinClass = e.'@mixinClass'
                if (mixinClass) {
                    extension.addMixin(pluginId, mixinClass)
                }
                def extensionClass = e.'@extensionClass'
                if (extensionClass) {
                    def extensionId = e.'@id'