throw new RuntimeException("No targetClass specified for extension provided by plugin '$pluginId'.")
                }
                def extension = extensions[targetClass]
                if (!extension) {
                    extension = new gradlebuild.docs.dsl.docbook.model.ClassExtensionMetaData(targetClass)
                    extensions[targetClass] = extension
                }
                def mixinClass = e.'@mixinClass'

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package gradlebuild.docs.dsl.docbook.model

/**
 * Represents the documentation model for extensions contributed by a given plugin.
 */
class ClassExtensionDoc {
    private final Set<ClassDoc> mixinClasses = []
    private final Map<String, ClassDoc> extensionClasses = [:]
    private final String pluginId

        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')
        ClassDoc extensionB = classDoc('org.gradle.ExtensionB')

 */
package gradlebuild.docs.dsl.docbook.model

class ExtensionMetaData {
    final String pluginId
    final String extensionId
    final String extensionClass

    ExtensionMetaData(String pluginId, String extensionId, String extensionClass) {
        this.pluginId = pluginId
        this.extensionId = extensionId
        this.extensionClass = extensionClass
    }

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

    def void addExtension(String plugin, String extension, String extensionClass) {
        extensionClasses.add(new ExtensionMetaData(plugin, extension, extensionClass))
    }